Ultraviolet curable type ink-jet ink composition, recording method and recording apparatus using same

ABSTRACT

Provided is a UV curable type ink-jet ink composition containing a monomer A which is expressed by the following general formula (I):
 
CH 2 ═CR 1 —COOR 2 —O—CH═CH—R 3   (I)
         (in the formula, R 1  is a hydrogen atom or methyl radical, R 2  is a bivalent organic residue radical having a carbon number in a range of 2 to 20, and R 3  is a hydrogen atom or a univalent organic residue radical having a carbon number in a range of 1 to 11), a compound B containing five or more (meth)acryloyl radicals per molecule, and a monofunctional (meth)acrylate C having an aromatic ring skeleton, wherein the monofunctional (meth)acrylate C which is in a range of 5 to 35 wt % with respect to the total weight of the ink composition is contained, wherein the compound B is in a range of 5 to 40 wt % with respect to the total weight of the ink composition, wherein the monomer A is in a range of 10 to 70 wt % with respect to the total weight of the ink composition.

CROSS REFERENCES TO RELATED APPLICATIONS

The entire disclosure of Japanese Patent Application No.: 2011-025920,filed Feb. 9, 2011 and 2010-251004, filed Nov. 9, 2010 and 2011-207187,filed Sep. 22, 2011 and 2010-260050, filed Nov. 22, 2010 are expresslyincorporated by reference herein.

BACKGROUND

1. Technical Field

The present invention relates to a UV curable type ink-jet inkcomposition and a recording method and a recording apparatus using thesame.

2. Related Art

In the related art, various types of a recording method of forming animage on a recording medium such as paper based on image data signalshave been used. Among the methods, in an ink jet type recording method,since the image is directly formed on the recording medium by ejectingink on only necessary portions by using an inexpensive apparatus, theink may be effectively used, and a running cost is low. In addition,since noise in the ink jet type recording method is small, the ink jettype recording method is a good recording method.

Recently, in order to form print with excellent water resistance,solvent resistance, abrasion resistance, and the like on the surface ofthe recording medium, in the ink jet type recording method, a UV curabletype ink-jet ink composition which is cured through illumination of anultraviolet rays has been used.

For example, JP-A-2009-96910 discloses a UV curable type ink-jet inkcomposition containing a polymerizable monomer made from one or morespecies selected from a group consisting of pentaerythritoltetraacrylate, dipentaerythritol hexa acrylate, or caprolactone modified(tris acryloxyethyl) isocyanurate, diethylene glycol mono vinyletheracrylate, isobornyl acrylate, tetraethylene glycol diacrylate,N-vinylpyrrolidone, triethylene glycol divinylether, andε-vinylcaprolactam, a predetermined coloring agent, and aphotopolymerization initiator.

In addition, in the related art, various types of a recording method offorming an image on a recording medium such as paper based on image datasignals have been used. Among the methods, in an ink jet type recordingmethod, since the image is directly formed on the recording medium byejecting ink on only necessary portions by using an inexpensiveapparatus, the ink may be effectively used, and running cost is low. Inaddition, since noise in the ink jet type recording method is small, theink jet type recording method is a good recording method.

Recently, in the ink jet type recording method, a UV curable type inkcomposition which is cured through illumination of an ultraviolet rayshas been used as an ink composition which may provide good waterresistance, solvent resistance, and abrasion resistance.

For example, Japanese Patent Nos. 4204333 and 3461501 disclose an activeenergy beam curable type ink jet printing ink containing a polymerizablemonomer such as (meth)acrylic acid 2-(vinyloxyethoxy) ethyl and aphotopolymerization initiator such as α-amino alkyl phenone.

In addition, JP-A-2009-57548 discloses a light curable type inkcomposition containing a resin-type polymer, a polymerizable monomersuch as (meth)acrylic acid 2-(vinyloxyethoxy) ethyl, and aphotopolymerization initiator such as an acylphosphine oxide.

However, in the case where a cured film is manufactured by using the UVcurable type ink-jet ink composition disclosed in JP-A-2009-96910, thefollowing problems occur. First, with respect to a thin film, in thecase of a radical polymerization reaction system, due to the influenceof oxygen inhibition, the curability deteriorates. Therefore, anadditional film is necessarily formed to be thick so that the oxygeninhibition does not occur at the time of printing, and thus, there is aproblem in that a quality of a printed image deteriorates. On the otherhand, particularly, with respect to black ink or yellow ink, in the caseof a thick film, a pigment has a strong tendency to absorb a portion ofan active radiation (particularly, UV region), and thus, although theactive radiation is illuminated, the energy necessary for completelycuring a coated film ejected on a recording medium may be insufficient.Therefore, in some cases, only a near surface portion of the coated filmis cured but an inner portion of the coated film is incompletely cured,or a relatively curing time is necessarily taken. Before a non-cured inkcomposition existing in an inner portion of the coated film is cured, ifthe non-cured ink composition flows irregularly, wrinkling occurs on thesurface of the film. Due to the wrinkling, there is a problem in that afilm characteristic of a thick film portion deteriorates.

SUMMARY

An advantage of some aspects of the invention is to provide a UV curabletype ink-jet ink composition of which the curability is excellent withrespect to both of a thin cured film and a thick cured film.

In addition, in the case where ink disclosed in Japanese Patent Nos.4204333 and 3461501 is cured through illumination of an ultraviolet rayshaving a light emitting peak in an area (350 to 400 nm) near visiblerays of light, there are problems in curability and abrasion resistanceand a degree of initial coloration of a cured film.

In addition, in the case where an ink composition disclosed inJP-A-2009-57548 is cured through illumination of an ultraviolet rayshaving a light emitting peak in an area near visible rays of light,there are point to be improved in a curability and abrasion resistanceand a degree of initial coloration of a cured film.

Another advantage of some aspects of the invention is to provide a UVcurable type ink composition which has a low degree of initialcoloration, excellent curability of ink, and excellent abrasionresistance of a cured film and a recording method using the UV curabletype ink composition.

The inventors have researched intensively in order to solve the problemdescribed above. As a result, it was found that the above problems maybe solved by a UV curable type ink-jet ink composition containing apredetermined amount of specified monomer and a compound containing fiveor more (meth)acryloyl radicals per molecule, and thus the invention hasbeen achieved.

In other words, the first invention is as follows.

[1] A UV curable type ink-jet ink composition containing a monomer Awhich is expressed by the following general formula (I):CH₂═CR¹—COOR²—O—CH═CH—R³  (I)(in the formula, R¹ is a hydrogen atom or methyl radical, R² is abivalent organic residue radical having a carbon number in a range of 2to 20, and R³ is a hydrogen atom or a univalent organic residue radicalhaving a carbon number in a range of 1 to 11), a compound B containingfive or more (meth)acryloyl radicals per molecule, and a monofunctional(meth)acrylate C having an aromatic ring skeleton, wherein themonofunctional (meth)acrylate C which is in a range of 5 to 35 wt % withrespect to the total weight of the ink composition is contained.

[2] In the UV curable type ink-jet ink composition according to [1], themonomer A is (meth)acrylic acid 2-(vinyloxyethoxy) ethyl.

[3] In the UV curable type ink-jet ink composition according to [1] or[2], the compound B contains at least one of a hexa (meth)acrylatecompound having six (meth)acryloyl radicals per molecule and apenta(meth)acrylate compound having five (meth)acryloyl radicals permolecule.

[4] In the UV curable type ink-jet ink composition according to any oneof [1] to [3], the compound B contains (meth)acrylate having adipentaerythritol skeleton.

[5] In the UV curable type ink-jet ink composition according to [3], thecompound B contains a dipentaerythritol hexa (meth)acrylate or adipentaerythritol penta (meth)acrylate.

[6] In the UV curable type ink-jet ink composition according to [1], thecompound B is in a range of 5 to 40 wt % with respect to the totalweight of the ink composition.

[7] In the UV curable type ink-jet ink composition according to any oneof [1] to [6], the monofunctional (meth)acrylate C having an aromaticring skeleton is at least one of benzyl (meth)acrylate and phenoxyethyl(meth)acrylate.

[8] In the UV curable type ink-jet ink composition according to any oneof [1] to [7], an acylphosphine oxide compound is contained as thephotopolymerization initiator.

[9] In the UV curable type ink-jet ink composition according to [8], theacylphosphine oxide compound which is in a range of 7 to 15 wt % withrespect to the total weight of the ink composition is contained as thephotopolymerization initiator.

[10] In the UV curable type ink-jet ink composition according to any oneof [1] to [9], the curing is performed through illumination ofultraviolet rays of which the light emitting peak wavelength is in arange of 350 to 420 nm with an illumination energy of equal to less than300 mJ/cm².

[11] In the UV curable type ink-jet ink composition according to any oneof [1] to [10], viscosity at 20° C. is in a range of 3 to 30 mPa·s.

[12] In the UV curable type ink-jet ink composition according to any oneof [1] to [11], the curing is performed in a state of a thin film havinga thickness of 0.5 to 3 μm.

[13] An ink jet recording method of ejecting the UV curable type ink-jetink composition of any one of [1] to [12] on a recording medium andcuring the ejected UV curable type ink-jet ink composition throughillumination using a UV-LED of which the light emitting peak wavelengthis in a range of 350 to 420 nm.

[14] An ink jet recording apparatus for ejecting the UV curable typeink-jet ink composition of any one of [1] to [12] on a recording mediumand curing the ejected UV curable type ink-jet ink composition throughillumination using a UV-LED of which the light emitting peak wavelengthis in a range of 350 to 420 nm.

In addition, the inventors have researched intensively in order to solvethe problem described above. As a result, it was found that the aboveproblems may be solved by a UV curable type ink composition containing apolymerizable compound and a photopolymerization initiator, wherein thepolymerizable compound contains a predetermined amount of acrylic acid2-(vinyloxyethoxy) ethyl and the photopolymerization initiator containsa predetermined amount of an acylphosphine oxide, and wherein theacylphosphine oxide contains a mono acylphosphine oxide, so that theinvention has been achieved.

In other words, the second invention is as follows.

[1] A UV curable type ink composition containing a polymerizablecompound and a photopolymerization initiator, wherein the polymerizablecompound contains a monomer A which is in a range of 40 to 90 wt % withrespect to the total amount of the ink composition and expressed by thefollowing general formula (I):CH₂═CR¹—COOR²—O—CH═CH—R³  (I)(in the formula, R¹ is a hydrogen atom or methyl radical, R² is abivalent organic residue radical having a carbon number in a range of 2to 20, and R³ is a hydrogen atom or a univalent organic residue radicalhaving a carbon number in a range of 1 to 11), and wherein thephotopolymerization initiator contains an acylphosphine oxide which isin a range of 7 to 12 wt % with respect to the total amount of the inkcomposition, and the acylphosphine oxide contains at least a monoacylphosphine oxide.

[2] In the UV curable type ink composition according to [1], the monomerA is acrylic acid 2-(vinyloxyethoxy) ethyl.

[3] In the UV curable type ink composition according to [1] or [2], thephotopolymerization initiator further contains a thioxanthone compoundwhich is in a range of 0.5 to 5 wt % with respect to the total amount ofthe ink composition.

[4] In the UV curable type ink composition according to [3], thethioxanthone compound is 2,4-diethyl thioxanthone.

[5] In the UV curable type ink composition according to any one of [1]to [4], the acylphosphine oxide contains a mono acylphosphine oxide orcontains a mono acylphosphine oxide and a bisacylphosphine oxide.

[6] In the UV curable type ink composition according to any one of [1]to [5], the curing may be performed through illumination of ultravioletrays of which the light emitting peak wavelength is in a range of 350 to400 nm with an illumination energy of less than 300 mJ/cm².

[7] In the UV curable type ink composition according to any one of [1]to [6], a phenoxyethyl (meth)acrylate which is in a range of 10 to 50 wt% with respect to the total amount of the ink composition is containedas the polymerizable compound.

[8] In the UV curable type ink composition according to any one of [1]to [7], the mono acylphosphine oxide which is in a range of equal to ormore than 1 wt % with respect to the total amount of the ink compositionis contained.

[9] A recording method using the UV curable type ink compositionaccording to any one of [1] to [8], wherein the UV curable type inkcomposition is attached on a recording medium, and the attached UVcurable type ink composition is illuminated with ultraviolet rays ofwhich the light emitting peak wavelength is in a range of 350 to 400 nmwith an illumination energy of less than 300 mJ/cm² by using a lightemitting diode.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, an embodiment for embodying a first invention will bedescribed in detail. In addition, the invention is not limited to theembodiments described hereinafter, and various modifications may beembodied within the scope of the invention.

In the specification, a “(meth)acrylate” denotes at least one ofacrylates and corresponding methacrylates; a “(meth)acryl” denotes atleast one of acryls and corresponding methacryls; and a “(meth)acryloyl”denotes acryloyls and corresponding methacryloyls.

In the specification, a “curability” denotes a property wherepolymerization curing is completed through light illumination in thepresence or absence of a photopolymerization initiator.

UV Curable Type Ink-Jet Ink Composition

An embodiment of the invention relates to a UV curable type ink-jet inkcomposition. The UV curable type ink-jet ink composition contains a(meth)acrylic acid ester (hereinafter, referred to as a “monomer A”)containing a predetermined amount of vinylether radicals which isexpressed by the following general formula (I):CH₂═CR¹—COOR²—O—CH═CH—R³  (I)(in the formula, R¹ is a hydrogen atom or methyl radical, R² is abivalent organic residue radical having a carbon number in a range of 2to 20, and R³ is a hydrogen atom or a univalent organic residue radicalhaving a carbon number in a range of 1 to 11), a compound (hereinafter,referred to as a “compound B”) containing five or more (meth)acryloylradicals per molecule, and a monofunctional (meth)acrylate C having anaromatic ring skeleton.

Hereinafter, additive agents (constituents) which are contained or maybe contained in a UV curable type ink-jet ink composition (hereinafter,simply referred to as an “ink composition”) according to the embodimentwill be described.

Polymerizable Compound

A polymerizable compound contained in the ink composition according tothe embodiment is polymerized due to an operation of aphotopolymerization initiator described later during a lightillumination period so as to allow printed ink to be cured.

1. Monomer A

As a necessary polymerizable compound in the embodiment, a monomer A isexpressed by the aforementioned general formula (I). The ink compositioncontains the monomer A, so that the curability of the ink may becomegood.

In the aforementioned general formula (I), as the bivalent organicresidue radical indicated by R² a straight-chain, branched, or cyclicalkylene radical having a carbon number in a range of 2 to 20, analkylene radical having a carbon number in a range of 2 to 20 and havingoxygen atoms in an ether bond and/or an ester bond in the structure, anda bivalent aromatic radical having a carbon number in a range of 6 to 11and being allowed to be substituted are very appropriately used. Amongthe materials, an alkylene radical having a carbon number in a range of2 to 6 such as an ethylene radical, an n-propylene radical, anisopropylene radical, and butylene radical and an alkylene radicalhaving a carbon number in a range of 2 to 9 and having oxygen atoms inan ether bond in the structure such as an oxyethylene radical, anoxy-n-propylene radical, an oxyisopropylene radical, and oxybutyleneradical are very appropriately used.

In the aforementioned general formula (I), as the univalent organicresidue radical having a carbon number in a range of 1 to 11 and beingindicated by R³, a straight-chain, branched, or cyclic alkyl radicalhaving a carbon number in a range of 1 to 10, and an aromatic radicalhaving a carbon number in a range of 6 to 11 and being allowed to besubstituted are very appropriately used. Among the materials, an alkylradical having a carbon number in a range of 1 to 2 such as a methylradical or an ethyl radical and an aromatic radical having a carbonnumber in a range of 6 to 8 such as a phenyl radical and a benzylradical are very appropriately used.

In the case where the aforementioned organic residue radical is aradical being allowed to be substituted, the substituent radicals may bedivided into radicals containing carbon atoms and radicals containing nocarbon atom. First, in the case where the substituent radical is aradical containing carbon atoms, the carbon atoms are counted as thecarbon number of the organic residue radical. The radical containingcarbon atoms is not limited to the following materials, but it mayinclude, for example, a carboxyl radical. In addition, the radicalcontaining no carbon atom is not limited to the following materials, butit may include, for example, a hydroxyl radical and a halo radical.

A specific example of the aforementioned monomer A is not limited to thefollowing materials, but it may include (meth)acrylic acid2-vinyloxyethyl, (meth)acrylic acid 3-vinyloxypropyl, (meth)acrylic acid1-methyl-2-vinyloxyethyl, (meth)acrylic acid 2-vinyloxypropyl,(meth)acrylic acid 4-vinyloxybutyl, (meth)acrylic acid1-methyl-3-vinyloxypropyl, (meth)acrylic acid 1-vinyloxymethyl propyl,(meth)acrylic acid 2-methyl-3-vinyloxypropyl, (meth)acrylic acid1,1′-dimethyl-2-vinyloxyethyl, (meth)acrylic acid 3-vinyloxybutyl,(meth)acrylic acid 1-methyl-2-vinyloxypropyl, (meth)acrylic acid2-vinyloxybutyl, (meth)acrylic acid 4-vinyloxycyclohexyl, (meth)acrylicacid 6-vinyloxyhexyl, (meth)acrylic acid 4-vinyloxymethylcyclohexylmethyl, (meth)acrylic acid 3-vinyloxymethyl cyclohexylmethyl,(meth)acrylic acid 2-vinyloxymethyl cyclohexylmethyl, (meth)acrylic acidp-vinyloxymethyl phenylmethyl, (meth)acrylic acid m-vinyloxymethylphenylmethyl, (meth)acrylic acid o-vinyloxymethyl phenylmethyl,(meth)acrylic acid 2-(vinyloxyethoxy) ethyl, (meth)acrylic acid2-(vinyloxyisopropoxy) ethyl, (meth)acrylic acid 2-(vinyloxyethoxy)propyl, (meth)acrylic acid 2-(vinyloxyethoxy) isopropyl, (meth)acrylicacid 2-(vinyloxyisopropoxy) propyl, (meth)acrylic acid2-(vinyloxyisopropoxy) isopropyl, (meth)acrylic acid2-(vinyloxyethoxyethoxy) ethyl, (meth)acrylic acid2-(vinyloxyethoxyisopropoxy) ethyl, (meth)acrylic acid2-(vinyloxyisopropoxyethoxy) ethyl, (meth)acrylic acid2-(vinyloxyisopropoxyisopropoxy) ethyl, (meth)acrylic acid2-(vinyloxyethoxyethoxy) propyl, (meth)acrylic acid2-(vinyloxyethoxyisopropoxy) propyl, (meth)acrylic acid2-(vinyloxyisopropoxyethoxy) propyl, (meth)acrylic acid2-(vinyloxyisopropoxyisopropoxy) propyl, (meth)acrylic acid2-(vinyloxyethoxyethoxy) isopropyl, (meth)acrylic acid2-(vinyloxyethoxyisopropoxy) isopropyl, (meth)acrylic acid2-(vinyloxyisopropoxyethoxy) isopropyl, (meth)acrylic acid2-(vinyloxyisopropoxyisopropoxy) isopropyl, (meth)acrylic acid2-(vinyloxyethoxyethoxyethoxy) ethyl, (meth)acrylic acid2-(vinyloxyethoxyethoxyethoxyethoxy) ethyl, (meth)acrylic acid2-(isoprophenoxyethoxy) ethyl, (meth)acrylic acid2-(isoprophenoxyethoxyethoxy) ethyl, (meth)acrylic acid2-(isoprophenoxyethoxyethoxyethoxy) ethyl, (meth)acrylic acid2-(isoprophenoxyethoxyethoxyethoxyethoxy) ethyl, (meth)acrylic acidpolyethylene glycol mono vinylether, and (meth)acrylic acidpolypropylene glycol mono vinylether.

Among the aforementioned materials, in order to secure more excellentcurability, (meth)acrylic acid 2-vinyloxyethyl, (meth)acrylic acid3-vinyloxypropyl, (meth)acrylic acid 1-methyl-2-vinyloxyethyl,(meth)acrylic acid 2-vinyloxypropyl, (meth)acrylic acid 4-vinyloxybutyl,(meth)acrylic acid 4-vinyloxycyclohexyl, (meth)acrylic acid5-vinyloxypentyl, (meth)acrylic acid 6-vinyloxyhexyl, (meth)acrylic acid4-vinyloxymethyl cyclohexylmethyl, (meth)acrylic acid p-vinyloxymethylphenylmethyl, (meth)acrylic acid 2-(vinyloxyethoxy) ethyl, (meth)acrylicacid 2-(vinyloxyethoxyethoxy) ethyl, (meth)acrylic acid2-(vinyloxyethoxyethoxyethoxy) ethyl are preferred.

Among the materials, in order to secure low viscosity, high flashingpoint, and excellent curability, at least one of (meth)acrylic acid2-(vinyloxyethoxy) ethyls, that is, acrylic acid 2-(vinyloxyethoxy)ethyl and methacrylic acid 2-(vinyloxyethoxy) ethyl is preferred, andthe former is more preferred. The (meth)acrylic acid 2-(vinyloxyethoxy)ethyl may include (meth)acrylic acid 2-(2-vinyloxyethoxy) ethyl and(meth)acrylic acid 2-(1-vinyloxyethoxy) ethyl. The acrylic acid2-(vinyloxyethoxy) ethyl may include acrylic acid 2-(2-vinyloxyethoxy)ethyl (hereinafter, referred to as a “VEER”) and acrylic acid2-(1-vinyloxyethoxy) ethyl.

With respect to the monomer A, one species may be individually used, ora combination of two or more species may be used.

The contained amount of the monomer A is not particularly limited withrespect to the total weight of the ink composition (100 wt %), but it ispreferably in a range of 10 to 75 wt %, more preferably in a range of 30to 75 wt %, particularly preferably in a range of 40 to 75 wt %,furthermore preferably in a range of 50 to 70 wt %. If the containedamount is within this range, the curability of the thin cured film ofwhich the thickness is a range of, for example, 0.5 to 3 μm may becomevery excellent.

The method of manufacturing the monomer A is not limited to thefollowing materials, but it may include an esterization method(Manufacturing Method C) of a (meth)acrylic acid and a hydroxylradical-containing vinylether, an esterization method (ManufacturingMethod D) of a (meth)acrylic acid halide and a hydroxylradical-containing vinylether, an esterization method (ManufacturingMethod E) of a (meth)acrylic acid anhydride and a hydroxylradical-containing vinylether, an ester exchanging method (ManufacturingMethod F) of a (meth)acrylic acid ester and a hydroxylradical-containing vinylether, an esterization method (ManufacturingMethod G) of a (meth)acryl acid and a halogen-containing vinylether, anesterization method (Manufacturing Method H) of a (meth)acrylic acidalkaline (earth) metal salt and a halogen-containing vinylether, avinylexchanging method (Manufacturing Method I) of a hydroxylradical-containing (meth)acrylic acid ester and a carboxylic acid vinyl,and an ether exchanging method (Manufacturing Method J) of a hydroxylradical-containing (meth)acrylic acid ester and an alkyl vinylether.

Among the materials, in order to further obtain a desired effect of theembodiment, the Manufacturing Method F is preferred.

2. Compound B

As a necessary polymerizable compound in the embodiment, the compound Bcontains 5 or more (meth)acryloyl radicals per molecule. In other words,the compound B is a 5-or-more-functional (meth)acrylate-based compound.In the ink composition according to the embodiment, the compound Btogether with the monomer A is contained as the polymerizable compound,so that the curability of the ink may become very good.

In addition, in order to secure more excellent curability, it ispreferable that the compound B have a hydroxyl radical in the molecule.

The 5-functional (meth)acrylate is not limited to the followingmaterials, but it may include at least one of, for example, sorbitolpenta(meth)acrylate, dipentaerythritol penta(meth)acrylate,ditrimethylol propane penta(meth)acrylate, propionic acid modifieddipentaerythritol penta(meth)acrylate, propionic acid modifiedtripentaerythritol penta(meth)acrylate, propionic acid modifiedtetrapentaerythritol penta(meth)acrylate, ethylene oxide (EO) adductsthereof, and propylene oxide (PO) adducts thereof.

The 6-functional (meth)acrylate is not limited to the followingmaterials, but it may include at least one of, for example, sorbitolhexa (meth)acrylate, ditrimethylol propane hexa acrylate,dipentaerythritol hexa (meth)acrylate, tripentaerythritol hexa(meth)acrylate, alkylene oxide modified hexa (meth)acrylate ofphosphazene, caprolactone modified dipentaerythritol hexa(meth)acrylate, propionic acid modified tripentaerythritol hexa(meth)acrylate, propionic acid modified tetrapentaerythritol hexa(meth)acrylate, EO adducts thereof, and PO adducts thereof.

The 7-or-more-functional (meth)acrylate is not limited to the followingmaterials, but it may include at least one of, for example,tripentaerythritol hepta(meth)acrylate, propionic acid modifiedtripentaerythritol hepta(meth)acrylate, propionic acid modifiedtetrapentaerythritol hepta(meth)acrylate, tripentaerythritolocta(meth)acrylate, propionic acid modified tetrapentaerythritolocta(meth)acrylate, tetrapentaerythritol nona(meth)acrylate, propionicacid modified tetrapentaerythritol nona(meth)acrylate,tetrapentaerythritol deca(meth)acrylate, pentapentaerythritolundeca(meth)acrylate, pentapentaerythritol dodeca(meth)acrylate, EOadducts thereof, and PO adducts thereof.

It is preferable that the compound B contain at least one of a6-functional (meth)acrylate, that is, a hexa (meth)acrylate compoundhaving six (meth)acryloyl radicals per molecule and a 5-functional(meth)acrylate, that is, a penta(meth)acrylate compound having five(meth)acryloyl radicals per molecule. In this case, the viscosity of theink becomes relatively low, and the curability of the ink becomes good.

In addition, it is preferable that the compound B contains a(meth)acrylate having a dipentaerythritol skeleton. In this case, thecurability of the ink becomes very excellent. The (meth)acrylate havinga dipentaerythritol skeleton may include dipentaerythritol hexa(meth)acrylate, dipentaerythritol penta(meth)acrylate, and the like.

The contained amount of the compound B is preferably in a range of 5 to40 wt % with respect to the total weight of the ink composition (100 wt%). If the contained amount is within this range, the curability of theink may become very excellent.

Among the materials, particularly, in the case where the compound B isdipentaerythritol hexa (meth)acrylate (more preferably dipentaerythritolhexa acrylate), the contained amount is preferably in a range of 5 to 30wt % with respect to the total weight of the ink composition (100 wt %),more preferably in a range of 5 to 15 wt %. If the contained amount iswithin this range, in the case where the cured film is a thin film ofwhich the thickness is in range of, for example, 0.5 to 3 μm, thecurability is excellent, and the ink may be formed to have a lowviscosity.

Among the materials, particularly, in the case where the compound B isdipentaerythritol penta(meth)acrylate (more preferably dipentaerythritolpentaacrylate), the contained amount is preferably in a range of 8 to 40wt % with respect to the total weight of the ink composition (100 wt %),more preferably in a range of 8 to 20 wt %. If the contained amount iswithin this range, in the case where the cured film is a thin film ofwhich the thickness is in range of, for example, 0.5 to 3 μm, thecurability is excellent, and the ink may be formed to have a lowviscosity.

With respect to the compound B, one species may be individually used, ora combination of two or more species may be used.

3. Monofunctional (Meth)Acrylate C Having Aromatic Ring Skeleton

As a necessary polymerizable compound in the embodiment, themonofunctional (meth)acrylate C has an aromatic ring skeleton. In theink composition according to the embodiment, the monofunctional(meth)acrylate C having an aromatic ring skeleton together with themonomer A and the compound B is contained as the polymerizable compound,so that the solubility of the photopolymerization initiator may becomegood and the curability of the ink may become good.

The monofunctional (meth)acrylate having an aromatic ring skeleton mayinclude, for example, benzyl (meth)acrylate, phenoxyethyl(meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate,phenoxydiethylene glycol (meth)acrylate, and the like.

As the monofunctional (meth)acrylate C having an aromatic ring skeleton,at least one of benzyl (meth)acrylate and phenoxyethyl (meth)acrylate ismore preferred, and at least one of benzyl acrylate and phenoxyethylacrylate is furthermore preferred. In this case, the viscosity of theink becomes low, and the solubility of the initiator becomes good.

With respect to at least one of the monofunctional (meth)acrylates Chaving an aromatic ring skeleton contained in the ink composition, thecontained amount is in the case where 5 to 35 wt % with respect to thetotal weight of the ink composition (100 wt %), preferably 5 to 30 in arange of wt %. If the contained amount is within this range, thesolubility of the photopolymerization initiator becomes good, and theviscosity of the ink may become low while maintaining the curability ina good state.

With respect to the aforementioned the monofunctional (meth)acrylate Chaving an aromatic ring skeleton, one species may be individually used,or a combination of two or more species may be used.

Other Polymerizable Compounds

In the embodiment, the aforementioned other polymerizable compounds(hereinafter, referred to as “other polymerizable compounds”) may befurther contained. As other polymerizable compounds, various types ofmonofunctional, bifunctional, trifunctional, or higher multifunctionalmonomers and oligomers in the related art may be used. The monomer mayinclude, for example, a (meth)acryl acid, unsaturated carboxylic acidssuch as itaconic acid, crotonic acid, isocrotonic acid, and maleic acidor salts thereof, esters, urethanes, amides and anhydrides thereof,acrylonitril, styrene, various types of unsaturated polyesters,unsaturated polyethers, unsaturated polyamides, and unsaturatedurethanes. In addition, the oligomer may include, for example, anoligomer made from the aforementioned monomer such as a straight-chainacryl oligomer, an epoxy (meth)acrylate, an oxetane (meth)acrylate, analiphatic urethane (meth)acrylate, an aromatic urethane (meth)acrylate,an polyester (meth)acrylate.

In addition, as another monofunctional monomer or multifunctionalmonomer, an N-vinylcompound may be contained. The N-vinylcompound mayinclude N-vinylformamide, N-vinylcarbazole, N-vinylacetamide,N-vinylpyrrolidone, N-vinylcaprolactam, acryloyl morpholine, derivativesthereof, and the like.

Hereinafter, among other polymerizable compounds, specific examples of atetrafunctional or lower (meth)acryl acid ester, that is, atetrafunctional or lower (meth)acrylate will be described.

The monofunctional (meth)acrylate is not limited to the followingmaterials, but it may include, for example, isoamyl (meth)acrylate,stearyl (meth)acrylate, lauryl (meth)acrylate, octyl (meth)acrylate,decyl (meth)acrylate, isomiristyl (meth)acrylate, isostearyl(meth)acrylate, 2-ethyl hexyl-diglycol (meth)acrylate, 2-hydroxybutyl(meth)acrylate, butoxy ethyl (meth)acrylate, ethoxydiethylene glycol(meth)acrylate, methoxydiethylene glycol (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, methoxypropylene glycol(meth)acrylate, tetrahydrofurfuryl (meth)acrylate, isobornyl(meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl(meth)acrylate, lactone-modified flexible (meth)acrylate, t-butylcyclohexyl (meth)acrylate, dicyclopentanyl (meth)acrylate, anddicyclopentenyl oxyethyl (meth)acrylate.

The bifunctional (meth)acrylate is not limited to the followingmaterials, but it may include, for example, 1,6-hexane dioldi(meth)acrylate, 1,10-decane diol di(meth)acrylate, neopentyl glycoldi(meth)acrylate, 2,4-dimethyl-1,5-pentane diol di(meth)acrylate, butylethyl propane diol (meth)acrylate, ethoxylated cyclohexanemethanoldi(meth)acrylate, polyethylene glycol di(meth)acrylate,oligoethylene glycol di(meth)acrylate, ethylene glycol di(meth)acrylate,2-ethyl-2-butyl butane diol di(meth)acrylate, hydroxy pivalic acidneopentyl glycol di(meth)acrylate, EO (ethylene oxide) modifiedbisphenol A di(meth)acrylate, bisphenol F polyethoxy di(meth)acrylate,polypropylene glycol di(meth)acrylate, oligopropylene glycoldi(meth)acrylate, 1,4-butane diol di(meth)acrylate, 2-ethyl-2-butylpropane diol di(meth)acrylate, 1,9-nonane di(meth)acrylate, propoxylatedethoxylated bisphenol A di(meth)acrylate, and tricyclodecanedi(meth)acrylate.

The trifunctional (meth)acrylate is not limited to the followingmaterials, but it may include, for example, trimethylol propane tri(meth)acrylate, trimethylol ethane tri (meth)acrylate, alkylene oxidemodified tri (meth)acrylate of trimethylol propane, pentaerythritol tri(meth)acrylate, dipentaerythritol tri (meth)acrylate, trimethylolpropane tri ((meth)acryloyl oxypropyl)ether, isocyanuric acid alkyleneoxide modified tri (meth)acrylate, propionic acid dipentaerythritol tri(meth)acrylate, tri ((meth)acryloyl oxyethyl) isocyanurate, hydroxypivalic aldehyde modified dimethylol propane tri (meth)acrylate,sorbitol tri (meth)acrylate, glyceryl propoxy tri (meth)acrylate,propoxylated trimethylol propane tri (meth)acrylate, ethoxylatedglycerin triacrylate, and caprolactone modified trimethylol propane tri(meth)acrylate.

The tetrafunctional (meth)acrylate is not limited to the followingmaterials, but it may include, for example, pentaerythritoltetra(meth)acrylate, sorbitol tetra(meth)acrylate, ditrimethylol propanetetra(meth)acrylate, propionic acid dipentaerythritoltetra(meth)acrylate, and ethoxylated pentaerythritoltetra(meth)acrylate.

In addition, among the other polymerizable compounds, the monofunctional(meth)acrylate may have one or more types of skeletons selected from agroup consisting of an aromatic ring skeleton, a saturated alicyclicskeleton, and an unsaturated alicyclic skeleton. By allowing the otherpolymerizable compound to be the monofunctional (meth)acrylate having askeleton, the viscosity of the ink composition may be lowered. Themonofunctional (meth)acrylate having a saturated alicyclic skeleton mayinclude, for example, isobornyl (meth)acrylate, t-butyl cyclohexyl(meth)acrylate and dicyclopentanyl (meth)acrylate. In addition, themonofunctional (meth)acrylate having an unsaturated alicyclic skeletonmay include, for example, dicyclopentenyl oxyethyl (meth)acrylate.

With respect to the aforementioned other polymerizable compounds, onespecies may be individually used, or a combination of two or morespecies may be used.

In the case where the aforementioned other polymerizable compounds arecontained, the contained amount is not limited, but it is in a range ofequal to or more than 5 wt % with respect to the total weight of the inkcomposition (100 wt %), preferably in a range of 5 to 40 wt %.

Photopolymerization Initiator

The photopolymerization initiator contained in the ink compositionaccording to the embodiment is used to perform printing by curing theink existing on the surface of the recording medium by thephotopolymerization through illumination of the ultraviolet rays. Byusing the ultraviolet rays (UV) as the illumination light, it ispossible to obtain excellent stability and to suppress the cost of thelight source lamp. Although a material which generates active speciessuch as radicals or cations by the energy of the light (ultravioletrays) to initiate the polymerization of the polymerizable compound maybe used without limitation, a photoradical polymerization initiator or aphoto-cation polymerization initiator may be used. Among them, thephotoradical polymerization initiator may be preferably used.

The aforementioned photoradical polymerization initiator may include forexample, aromatic ketones, acylphosphine oxide compounds, aromatic oniumsalt compounds, organic peroxides, thio compounds (thioxanthonecompounds, compounds containing a thio phenyl radical, or the like),hexa alirubi imidazole compounds, ketoxime ester compounds, boratecompounds, ajinium compounds, metallocene compounds, active estercompounds, compounds having a carbon halogen bond, and alkyl aminecompounds.

Among the materials, particularly in order to secure good curability ofthe ink, at least one of an acylphosphine oxide compound and athioxanthone compound is preferred, and the acylphosphine oxide compoundand the thioxanthone compound are more preferred.

A specific example of the photoradical polymerization initiator mayinclude acetophenone, acetophenone benzyl ketal, 1-hydroxycyclohexylphenyl ketone, 2,2-dimethoxy-2-phenyl acetophenone, xanthone,fluorenone, benzaldehyde, fluorene, anthraquinone, triphenyl amine,carbazole, 3-methyl acetophenone, 4-chloro benzophenone, 4,4′-dimethoxybenzophenone, 4,4′-diamino benzophenone, Michler's ketone, benzoinpropyl ether, benzoin ethyl ether, benzyl dimethyl ketal, 1-(4-isopropylphenyl)-2-hydroxy-2-methyl propane-1-one, 2-hydroxy-2-methyl-1-phenylpropane-1-one, thioxanthone, diethyl thioxanthone, 2-isopropylthioxanthone, 2-chloro thioxanthone, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholino propane 1-one, bis(2,4,6-trimethylbenzoyl)phenyl phosphine oxide, 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide, 2,4-diethyl thioxanthone, andbis-(2,6-dimethoxybenzoyl)-2,4,4-trimethyl pentyl phosphine oxide.

Among the materials, the 2,4,6-trimethyl benzoyl-diphenyl-phosphineoxide, the bis(2,4,6-trimethyl benzoyl) phenyl phosphine oxide, and the2,4-diethyl thioxanthone are very appropriately used.

A commercialized product of the photoradical polymerization initiatormay include, for example, IRGACURE 651 (2,2-dimethoxy-1,2-diphenylethane-1-one), IRGACURE 184 (1-hydroxy-cyclohexyl-phenyl-ketone),DAROCUR 1173 (2-hydroxy-2-methyl-1-phenyl-propane-1-one), IRGACURE 2959(1-[4-(2-hydroxyethoxy)phenyl]-2-hydroxy-2-methyl-1-propane-1-one),IRGACURE 127 (2-hydroxy-1-{4-[4-(2-hydroxy-2-methylpropionyl)-benzyl]phenyl}-2-methyl-propane-1-one}, IRGACURE 907(2-methyl-1-(4-methyl thio phenyl)-2-morpholino propane 1-one), IRGACURE369 (2-benzyl-2-dimethyl amino-1-(4-morpholino phenyl)-butanone1),IRGACURE 379 (2-(dimethyl amino)-2-[(4-methylphenyl)methyl]-1-[4-(4-morpholinyl)phenyl]-1-butanone), DAROCUR TPO(2,4,6-trimethyl benzoyl-diphenyl-phosphine oxide), IRGACURE 819(bis(2,4,6-trimethyl benzoyl)phenyl phosphine oxide), IRGACURE 784(bis(η5-2,4-cyclopentadiene-1-yl)-bis(2,6-difluoro-3-(1H-pyrrol1-yl)phenyl)titanium), IRGACURE OXE 01 (1,2-octane dione, 1-[4-(phenylthio)-, 2-(O-benzoyl oxime)]), IRGACURE OXE 02 (ethanone,1-[9-ethyl-6-(2-methyl benzoyl)-9H-carbazole 3-yl]-, 1-(O-acetyloxime)), IRGACURE 754 (a mixture of oxyphenyl acetic acid,2-[2-oxo-2-phenyl acetoxyethoxy]ethyl ester and oxyphenyl acetic acid,2-(2-hydroxyethoxy)ethyl ester) (trade names of products manufactured byBASF), KAYACURE DETX-S (2,4-diethyl thioxanthone) (trade name of productmanufactured by NIPPON KAYAKU CO., LTD.), Lucirin TPO, LR8893, LR8970(trade names of products manufactured by BASF), Uvecryl P36 (trade nameof product manufactured by UCB), and the like.

With respect to the photopolymerization initiator, one species may beindividually used, or a combination of two or more species may be used.

With respect to the photopolymerization initiator, in order to securegood curability of the ink and to prevent the melt remaining of thephotopolymerization initiator or the coloring derived from thephotopolymerization initiator, the contained amount thereof ispreferably in a range of 1 to 20 wt % with respect to the total weightof the ink composition (100 wt %).

In addition, although addition of the photopolymerization initiator maybe omitted by using a photopolymerizable compound as the aforementionedpolymerizable compound, the photopolymerization initiator is verypreferably used since the initiation of the polymerization may be easilyadjusted.

In addition, in the case where the photopolymerization initiatorcontains an acylphosphine oxide compound, the contained amount thereofis preferably in a range of 7 to 15 wt % with respect to the totalweight of the ink composition (100 wt %), more preferably in a range of8 to 14%, particularly preferably in a range of 9 to 13%. If thecontained amount is within this range, the curability of the inkcomposition may become more excellent, and the solubility to the inkcomposition may become good.

In addition, in the cased where the photopolymerization initiatorcontains a thioxanthone compound, the contained amount thereof ispreferably in a range of 0.5 to 4 wt % with respect to the total weightof the ink composition (100 wt %), more preferably in a range of 1 to 3wt %. If the contained amount is within this range, the curability ofthe ink composition may become more excellent.

Coloring Material

The ink composition according to the embodiment may further contain acoloring material. With respect to the coloring material, at least oneof a pigment and a dye may be used.

Pigment

In the embodiment, a pigment may be used as the coloring material, sothat it is possible to improve the light resistance of the inkcomposition. With respect the pigment, both of an inorganic pigment andan organic pigment may be used.

As the inorganic pigment, carbon black (C. I. Pigment Black 7) such as afurnace black, a lamp black, an acetylene black, and a channel black,iron oxide, and titanium oxide may be used.

The organic pigment may include azo pigments such as insoluble azopigments, condensed azo pigments, azoreki, and chelate azo pigments,polycyclic pigments such as phthalocyanine pigments, perylene andperinone pigments, anthraquinone pigments, quinacridone pigments,dioxane pigments, thioindigo pigments, isoindolinone pigments, andquinophthalone pigments, dye chelates (for example, basic dye typechelates, acidic dye type chelates, or the like), stained lakes (basicdye type lakes and acidic dye type lakes), nitro pigments, nitrosopigments, aniline blacks, and daylight fluorescent pigments.

More specifically, the carbon black used as the black ink may includeNo. 2300, No. 900, MCF88, No. 33, No. 40, No. 45, No. 52, MA7, MA8,MA100, No. 2200B, and the like (trade names of products manufactured byMITSUBISHI CHEMICAL CORPORATION), Raven 5750, Raven 5250, Raven 5000,Raven 3500, Raven 1255, Raven 700, and the like (trade names of productsmanufactured by CARBON COLUMBIA), Regal 400R, Regal 330R, Regal 660R,Mogul L, Monarch 700, Monarch 800, Monarch 880, Monarch 900, Monarch1000, Monarch 1100, Monarch 1300, Monarch 1400, and the like (tradenames of products manufactured by CABOT JAPAN K.K.), and Color BlackFW1, Color Black FW2, Color Black FW2V, Color Black FW18, Color BlackFW200, Color Black S150, Color Black S160, Color Black S170, Printex 35,Printex U, Printex V, Printex 140U, Special Black 6, Special Black 5,Special Black 4A, Special Black 4, and the like (trade names of productsmanufactured by DEGUSSA).

The pigment used as the white ink may include C. I. Pigment White 6, 18,21.

The pigment used as the yellow ink may include C. I. Pigment Yellow 1,2, 3, 4, 5, 6, 7, 10, 11, 12, 13, 14, 16, 17, 24, 34, 35, 37, 53, 55,65, 73, 74, 75, 81, 83, 93, 94, 95, 97, 98, 99, 108, 109, 110, 113, 114,117, 120, 124, 128, 129, 133, 138, 139, 147, 151, 153, 154, 167, 172,180.

The pigment used as the magenta ink may include C. I. Pigment Red 1, 2,3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 17, 18, 19, 21, 22, 23, 30,31, 32, 37, 38, 40, 41, 42, 48 (Ca), 48 (Mn), 57 (Ca), 57:1, 88, 112,114, 122, 123, 144, 146, 149, 150, 166, 168, 170, 171, 175, 176, 177,178, 179, 184, 185, 187, 202, 209, 219, 224, 245, and C. I. PigmentViolet 19, 23, 32, 33, 36, 38, 43, 50.

The pigment used as the cyan ink may include C. I. Pigment Blue 1, 2, 3,15, 15:1, 15:2, 15:3, 15:34, 15:4, 16, 18, 22, 25, 60, 65, 66, and C. I.Vat Blue 4, 60.

In addition, the pigment excluding the magenta, cyan, and yellowpigments may include, for example, C. I. Pigment Green 7, 10, C. I.Pigment Brown 3, 5, 25, 26, and C. I. Pigment Orange 1, 2, 5, 7, 13, 14,15, 16, 24, 34, 36, 38, 40, 43, 63.

With respect to the pigment, one species may be individually used, ortwo or more species may be simultaneously used.

In the case where the aforementioned pigment is used, the averageparticle diameter is preferably equal to or less than 300 nm, morepreferably in a range of 50 to 200 nm. If the average particle diameteris within the aforementioned range, reliability such as ejectionstability or dispersion stability of the ink composition may become moreexcellent, and an image having an excellent quality of image may beformed. Herein, in the specification, the average particle diameter ismeasured by a dynamic light scattering method.

Dye

In the embodiment, a dye may be used as the coloring material. The dyeis not particularly limited, and an acidic dye, a direct dye, a reactivedye, and a basic dye may be used. The dye may include, for example, C.I. Acid Yellow 17, 23, 42, 44, 79, 142, C. I. Acid Red 52, 80, 82, 249,254, 289, C. I. Acid Blue 9, 45, 249, C. I. Acid Black 1, 2, 24, 94, C.I. Food Black 1, 2, C. I. Direct Yellow 1, 12, 24, 33, 50, 55, 58, 86,132, 142, 144, 173, C. I. Direct Red 1, 4, 9, 80, 81, 225, 227, C. I.Direct Blue 1, 2, 15, 71, 86, 87, 98, 165, 199, 202, C. I. Direct Black19, 38, 51, 71, 154, 168, 171, 195, C. I. Reactive Red 14, 32, 55, 79,249, and C. I. Reactive Black 3, 4, 35.

With respect to the dye, one species may be individually used, or two ormore species may be simultaneously used.

In order to obtain an excellent obliterating property and colorreproducibility, the contained amount of the coloring material ispreferably in a range of 0.5 to 10 wt % with respect to the total weightof the ink composition (100 wt %).

Dispersing Agent

In the case where the ink composition according to the embodimentcontains a pigment, in order to secure better pigment dispersibility, adispersing agent may further contained. The dispersing agent is notparticularly limited, but it may include, for example, a dispersingagent such as a macromolecular dispersing agent which is well used tomanufacture a pigment dispersion liquid. A specific example may includeone or more species of polyoxy alkylene polyalkylene polyamine, avinyl-based polymer and a copolymer, an acryl-based polymer and acopolymer, a polyester, a polyamide, a polyimide, a poly urethane, anamino-based polymer, a silicon-containing polymer, an sulfur-containingpolymer, a fluorine-containing polymer, and an epoxy resin as a mainconstituent. A commercialized product of the macromolecular dispersingagent may include Discoall series manufactured by DAI-ICHI KOGYO SEIYAKUCO., LTD., Solsperse series (Solsperse 36000 or the like) manufacturedby LUBRIZOL CORPORATION, and Disperbyk series manufactured by BYKCHEMIE.

Slip Agent

In order to obtain excellent abrasion resistance, the ink compositionaccording to the embodiment may further contain a slip agent(surfactant). The slip agent is not particularly limited. For example,as a silicon-based surfactant, a polyester modified silicon or apolyether modified silicon may be used. Particularly, it is preferablethat a polyether modified polydimethyl siloxane or a polyester modifiedpolydimethyl siloxane be used. A specific example may include BYK-347,BYK-348, BYK-UV3500, 3510, 3530, 3570 (manufactured by BYK JAPAN K.K.).

Polymerization Inhibitor

The ink composition according to the embodiment may further contain apolymerization inhibitor. By adding the polymerization inhibitor to theink composition, the preservation stability of the ink composition isimproved. The polymerization inhibitor is not particularly limited, butit may include, for example, at least one or more species selected froma group consisting of a phenol compound, a hydroquinone compound, and aquinine compound. A specific example of the polymerization inhibitor mayinclude hydroquinone, p-methoxyphenol, cresol, t-butyl catechol,3,5-di-t-butyl-4-hydroxy toluene, 2,2′-methylene bis(4-methyl-6-t-butylphenol), 2,2′-methylene bis(4-ethyl-6-butyl phenol), 4,4′-thiobis(3-methyl-6-t-butyl phenol).

As a commercialized product of the polymerization inhibitor, IRGASTABUV10 and UV22 (trade names of products manufactured by BASF) or the likemay be used.

Other Additive Agents

The ink composition according to the embodiment may contain otheradditive agents (constituents) besides the additive agents describedabove. The constituents are not particularly limited and may include,for example a polymerization accelerator, a penetration enhancer, awetting agent (humectant), and other additive agents which are wellknown in the related art. Other additive agents listed above mayinclude, for example, a fixer, a fungicide, an antiseptic agent, anantioxidant, an ultraviolet ray absorber, a chelate agent, a pHadjuster, and a viscosity improver which are well known in the relatedart.

Recording Medium

A recording material may be obtained by ejecting the UV curable typeink-jet ink composition according to the embodiment on the recordingmedium by an ink jet recording method described later. The recordingmedium may include, for example, an absorptive recording medium or anon-absorptive recording medium. The ink jet recording method accordingto the embodiment may be applied to a variety of the recording mediahaving various absorption performances ranging from a non-absorptiverecording medium which may be easily penetrated by penetrate an aqueousink composition thereto to an absorptive recording medium which may notbe easily penetrated by an aqueous ink composition thereto. However, inthe case where the ink composition is applied to the non-absorptiverecording medium, a drying process may be necessarily provided after thecuring through the illumination of the ultraviolet rays.

The absorptive recording medium is not particularly limited, but it mayinclude, for example, a plain paper such an electro-photographic paperhaving a high permeability of aqueous ink, ink jet paper (ink jetdedicated paper having an ink absorption layer made from silicaparticles or aluminum particles or an ink absorption layer made from ahydrophilic polymer such as polyvinylalcohol (PVA) orpolyvinylpyrrolidone (PVP)), art paper used for general offset printinghaving a relatively low permeability of aqueous ink, coat paper, castpaper, and the like.

The non-absorptive recording medium is not particularly limited, but itmay include, for example, a plastic film or plate such as polyvinyl,chloride, polyethylene, polypropylene, and polyethylene terephthalate(PET), a metal plate such as iron, silver, copper, and aluminum, a metalplate or a plastic film produced by depositing various metals, an alloyplate such as stainless steel or brass, or the like.

Ink Jet Recording Method

The UV curable type ink-jet ink composition according to the embodimentmay be used for an ink jet recording method. The ink jet recordingmethod includes an ejection process for ejecting an ink composition on arecording medium and a curing process for curing the ink composition byilluminating the ink composition ejected by the ejection process with anultraviolet rays. In this manner, a coated film (cured film) is formedwith the ink composition cured on the recording medium.

Ejection Process

In the ejection process, an ink jet recording apparatus in the relatedart may be used. In order to secure good ejection stability at the timeof ejecting the ink composition, the viscosity of the ink composition at20° C. is preferably in a range of 3 to 30 mPa·s, more preferably in arange of 5 to 15 mPa·s.

Since the viscosity of the UV curable type ink-jet ink compositionaccording to the embodiment is higher than that of an aqueous inkcomposition which is used as a general ink-jet ink, the viscosity isgreatly changed according to a change in temperature at the time ofejection. The change in viscosity of the ink has much influence on achange in size of liquid droplets and a change in ejection rate ofliquid droplets, and furthermore, it may lead to deterioration inquality of image. Therefore, it is preferable that the temperature ofthe ink at the time of ejection is maintained as constant as possible.

Curing Process

Next, in the curing process, the ink composition ejected on therecording medium is cured through illumination of the ultraviolet rays(light). This is because the photopolymerization initiator contained inthe ink composition is dissolved through illumination of the ultravioletrays to generate initiating species such as radicals, acids, and basesand the polymerization reaction of the photopolymerizable compound isprompted by the function of the initiating species. Otherwise, this isbecause the polymerization reaction of the photopolymerizable compoundis initiated though the illumination of the ultraviolet rays. At thistime, if a sensitizing dye together with the photopolymerizationinitiator exist in the ink composition, the sensitizing dye in thesystem absorbs the ultraviolet rays to be in the excited state, and thedissolution of the photopolymerization initiator is precipitated byallowing the sensitizing dye to be in contact with thephotopolymerization initiator, so that it is possible to achieve themore sensitive curing reaction.

As an ultraviolet ray source, a mercury lamp, a gas-solid laser, and thelike are mainly used. As a light source used for the curing of the UVcurable type ink-jet ink composition, a mercury lamp and an a metalhalide lamp are widely known. On the other hand, currently, mercury-freesources are greatly preferred in terms of environmental protection, andreplacement with a GaN-based semiconductor ultra violet light emittingdevice is very useful from industrial and environmental points of view.In addition, the ultraviolet ray light emitting diode (UV-LED) and theultraviolet ray laser diode (UV-LD) has a small size, a long lifetime,and a high efficiency and is inexpensive, and thus, the sources areexpected to be used as a UV curable type ink jet light source. Among thesources, the UV-LED is preferred.

Herein, it is preferable that a UV curable type ink-jet ink compositionwhich may be cured through illumination of ultraviolet rays of which thelight emitting peak wavelength is preferably in a range of 350 to 420nm, more preferably in a range of 365 to 405 nm with an illuminationenergy which is preferably in a range of equal to or less than 300mJ/cm², more preferably in a range of 100 to 250 mJ/cm² be used. In thiscase, due to the composition of the ink composition according to theembodiment, the curing may be performed at a low energy and at a highrate. The illumination energy is calculated as a product of anillumination time and an illumination intensity. The illumination timemay be reduced according to the composition of the ink compositionaccording to the embodiment, and in this case, the printing speed isincreased. On the other hand, the illumination intensity may bedecreased according to the composition of the ink composition accordingto the embodiment, and in this case, a small-sized apparatus and costreduction may be implemented. In this case, the UV-LED is preferablyused for the ultraviolet ray illumination. Such an ink composition maybe obtained by containing a polymerizable compound of which thepolymerization is initiated through the ultraviolet ray illumination inthe wavelength range and a photopolymerization initiator which isdissolved through the ultraviolet ray illumination in the wavelengthrange.

In addition, it is preferable that a UV curable type ink-jet inkcomposition which may be cured in the state of a thin film of which thethickness is preferably in a range of 0.5 to 3 μm, more preferably in arange of 0.8 to 2.5 μm be used. In this case, due to the composition ofthe ink composition according to the embodiment, an image may be formedin a thin film, so that it is possible to obtain advantageous effect inthat a swelling appearance of the coated film is reduced. The inkcomposition may be obtained by using various methods described above.

In this manner, according to the embodiment, in both of a thin (forexample, the thickness is in a range of 0.5 to 3 μm) cured film and athick (for example, the thickness is in a range of equal to more than 10μm) cured film, it is possible to provide a UV curable type ink-jet inkcomposition having excellent curability. More specifically, with respectto a thin film of which the thickness is in a range of, for example, 0.5to 3 μm or dots of which the diameter is in a range of, for example, 0.5to 3 μm, the curability is improved. Therefore, the printing may beperformed so that the smaller ink droplets are attached to the recordingmedium, and thus, the quality of image is improved. In addition,particularly with respect to the black ink or the yellow ink, thecurability of the thick film (for example, the thickness is in a rangeof equal to or more 10 μm) is improved, so that it is possible tosuppress the occurrence of wrinkling. Therefore, the characteristics ofthe coated film of the ink are improved.

Ink Jet Recording Apparatus

The UV curable type ink-jet ink composition according to the embodimentmay be used for an ink jet recording apparatus. The ink jet recordingapparatus performs recording by the aforementioned ejection process forejecting an ink composition on a recording medium and the aforementionedcuring process for curing the ink composition by illuminating the inkcomposition ejected by the ejection process with an ultraviolet rays. Inthis manner, the ink jet recording apparatus is a recording apparatuswhich forms a coated film (cured film) with the ink composition cured onthe recording medium.

Hereinafter, an embodiment for embodying a second invention will bedescribed in detail. In addition, the invention is not limited to theembodiments described hereinafter, and various modifications may beembodied within the scope of the invention.

In the specification, a “(meth)acrylate” denotes at least one ofacrylates and corresponding methacrylates, and a “(meth)acryl” denotesat least one of acryls and corresponding methacryls.

In the specification, “curability” denotes a property where a materialis cured through light sensitization. “Abrasion resistance” denotes aproperty where a cured film (image surface) of a recording material ishard to scratch. In addition, a degree of the abrasion resistance isproportional to a hardness of the cured film. “Color stability” aproperty where, as seen in a time sequence after printing, L*a*b* in CIELab (L*a*b* colorimetric system) is barely changed from L*a*b* justafter the printing. “Ejection stability” denotes a property where inkdroplets are always stably ejected from nozzles without clogging of thenozzles.

UV Curable Type Ink Composition

An embodiment of the invention relates to a UV curable type inkcomposition. The UV curable type ink composition contains apolymerizable compound and a photopolymerization initiator. Thepolymerizable compound contains a monomer A described later, which is ina range of 40 to 90 wt % with respect to the total amount of the inkcomposition. The photopolymerization initiator contains an acylphosphineoxide which is in a range of 7 to 12 wt % with respect to the totalamount of the ink composition. The acylphosphine oxide contains a monoacylphosphine oxide.

Hereinafter, additive agents (constituents) which are contained or maybe contained in the UV curable type ink composition (hereinafter, simplyreferred to as an “ink composition”) according to the embodiment will bedescribed.

Polymerizable Compound

The polymerizable compound contained in the ink composition according tothe embodiment are polymerized due to the operation of thephotopolymerization initiator described later during an ultraviolet rayillumination period, so that the printed ink may be cured.

Monomer A

As a necessary polymerizable compound in the embodiment, a monomer A isa vinylether radical-containing (meth)acrylic acid ester and isexpressed by the following general formula (I).CH₂═CR¹—COOR²—O—CH═CH—R³  (I)(in the formula, R¹ is a hydrogen atom or methyl radical, R² is abivalent organic residue radical having a carbon number in a range of 2to 20, and R³ is a hydrogen atom or a univalent organic residue radicalhaving a carbon number in a range of 1 to 11).

The ink composition contains the monomer A, so that the curability ofthe ink may become good.

In the aforementioned general formula (I), as the bivalent organicresidue radical having a carbon number in a range of 2 to 20 and beingindicated by R² a straight-chain, branched, or cyclic alkylene radicalhaving a carbon number in a range of 2 to 20, an alkylene radical havinga carbon number in a range of 2 to 20 and having oxygen atoms in anether bond and/or an ester bond in the structure, and a bivalentaromatic radical having a carbon number in a range of 6 to 11 and beingallowed to be substituted are very appropriately used. Among thematerials, an alkylene radical having a carbon number in a range of 2 to6 such as an ethylene radical, an n-propylene radical, an isopropyleneradical, and a butylene radical, and an alkylene radical having a carbonnumber in a range of 2 to 9 and having oxygen atoms in an ether bond inthe structure such as an oxyethylene radical, an oxy-n-propyleneradical, an oxyisopropylene radical, and oxybutylene radical are veryappropriately used.

In the aforementioned general formula (I), as the univalent organicresidue radical having a carbon number in a range of 1 to 11 and beingindicated by R³, a straight-chain, branched or cyclic alkyl radical,having 1 to 10 oxygen atoms, and an aromatic radical having 6 to 11oxygen atoms and being allowed to be substituted are very appropriatelyused. Among the materials, an alkyl radical having a carbon number in arange of 1 to 2 such as a methyl radical or an ethyl radical and anaromatic radical having a carbon number in a range of 6 to 8 such as aphenyl radical and a benzyl radical are very appropriately used.

In the case where the aforementioned organic residue radical is aradical being allowed to be substituted, the substituent radicals may bedivided into radicals containing carbon atoms and radicals containing nocarbon atom. First, in the case where the substituent radical is aradical containing carbon atoms, the carbon atoms are counted as thecarbon number of the organic residue radical. The radical containingcarbon atoms is not limited to the following materials, but it mayinclude, for example, a carboxyl radical, an alkoxy radical, and thelike. In addition, the radical containing no carbon atom is not limitedto the following materials, but it may include, for example, a hydroxylradical and a halo radical.

The aforementioned monomer A is not limited to the following materials,but it may include, for example, (meth)acrylic acid 2-vinyloxyethyl,(meth)acrylic acid 3-vinyloxypropyl, (meth)acrylic acid1-methyl-2-vinyloxyethyl, (meth)acrylic acid 2-vinyloxypropyl,(meth)acrylic acid 4-vinyloxybutyl, (meth)acrylic acid1-methyl-3-vinyloxypropyl, (meth)acrylic acid 1-vinyloxymethyl propyl,(meth)acrylic acid 2-methyl-3-vinyloxypropyl, (meth)acrylic acid1,1-dimethyl-2-vinyloxyethyl, (meth)acrylic acid 3-vinyloxybutyl,(meth)acrylic acid 1-methyl-2-vinyloxypropyl, (meth)acrylic acid2-vinyloxybutyl, (meth)acrylic acid 4-vinyloxycyclohexyl, (meth)acrylicacid 6-vinyloxyhexyl, (meth)acrylic acid 4-vinyloxymethylcyclohexylmethyl, (meth)acrylic acid 3-vinyloxymethyl cyclohexylmethyl,(meth)acrylic acid 2-vinyloxymethyl cyclohexylmethyl, (meth)acrylic acidp-vinyloxymethyl phenylmethyl, (meth)acrylic acid m-vinyloxymethylphenylmethyl, (meth)acrylic acid o-vinyloxymethyl phenylmethyl,(meth)acrylic acid 2-(vinyloxyethoxy) ethyl, (meth)acrylic acid2-(vinyloxyisopropoxy) ethyl, (meth)acrylic acid 2-(vinyloxyethoxy)propyl, (meth)acrylic acid 2-(vinyloxyethoxy) isopropyl, (meth)acrylicacid 2-(vinyloxyisopropoxy) propyl, (meth)acrylic acid2-(vinyloxyisopropoxy) isopropyl, (meth)acrylic acid2-(vinyloxyethoxyethoxy) ethyl, (meth)acrylic acid2-(vinyloxyethoxyisopropoxy) ethyl, (meth)acrylic acid2-(vinyloxyisopropoxyethoxy) ethyl, (meth)acrylic acid2-(vinyloxyisopropoxyisopropoxy) ethyl, (meth)acrylic acid2-(vinyloxyethoxyethoxy) propyl, (meth)acrylic acid2-(vinyloxyethoxyisopropoxy) propyl, (meth)acrylic acid2-(vinyloxyisopropoxyethoxy) propyl, (meth)acrylic acid2-(vinyloxyisopropoxyisopropoxy) propyl, (meth)acrylic acid2-(vinyloxyethoxyethoxy) isopropyl, (meth)acrylic acid2-(vinyloxyethoxyisopropoxy) isopropyl, (meth)acrylic acid2-(vinyloxyisopropoxyethoxy) isopropyl, (meth)acrylic acid2-(vinyloxyisopropoxyisopropoxy) isopropyl, (meth)acrylic acid2-(vinyloxyethoxyethoxyethoxy) ethyl, (meth)acrylic acid2-(vinyloxyethoxyethoxyethoxyethoxy) ethyl, (meth)acrylic acid2-(isoprophenoxyethoxy) ethyl, (meth)acrylic acid2-(isoprophenoxyethoxyethoxy) ethyl, (meth)acrylic acid2-(isoprophenoxyethoxyethoxyethoxy) ethyl, (meth)acrylic acid2-(isoprophenoxyethoxyethoxyethoxyethoxy) ethyl, (meth)acrylic acidpolyethylene glycol mono vinylether, and (meth)acrylic acidpolypropylene glycol mono vinylether.

Among the materials, in order to secure low viscosity, high flashingpoint, and excellent curability, at least one of (meth)acrylic acid2-(vinyloxyethoxy) ethyl, that is, acrylic acid 2-(vinyloxyethoxy) ethyland methacrylic acid 2-(vinyloxyethoxy) ethyl is preferred, and acrylicacid 2-(vinyloxyethoxy) ethyl is further preferred. The (meth)acrylicacid 2-(vinyloxyethoxy) ethyl may include (meth)acrylic acid2-(2-vinyloxyethoxy) ethyl and (meth)acrylic acid 2-(1-vinyloxyethoxy)ethyl. The acrylic acid 2-(vinyloxyethoxy) ethyl may include acrylicacid 2-(2-vinyloxyethoxy) ethyl and acrylic acid 2-(1-vinyloxyethoxy)ethyl. In addition, acrylic acid 2-(vinyloxyethoxy) ethyl is moreexcellent than methacrylic acid 2-(vinyloxyethoxy) ethyl in terms of thecurability.

The contained amount of the monomer A is in a range of 40 to 90 wt %with respect to the total amount of the ink composition (100 wt %),preferably in a range of 60 to 90 wt %, and more preferably in a rangeof 60 to 80 wt %. If the contained amount is within this range, thecurability of the ink and the abrasion resistance of the cured filmbecome excellent.

The method of manufacturing the monomer A is not limited to thefollowing materials, but it may include an esterization method(Manufacturing Method B) of a (meth)acrylic acid and a hydroxylradical-containing vinylether, an esterization method (ManufacturingMethod C) of a (meth)acrylic acid halide and a hydroxylradical-containing vinylether, an esterization method (ManufacturingMethod D) of a (meth)acrylic acid anhydride and a hydroxylradical-containing vinylether, an ester exchanging method (ManufacturingMethod E) of a (meth)acrylic acid ester and a hydroxylradical-containing vinylether, an esterization method (ManufacturingMethod F) of a (meth)acryl acid and a halogen-containing vinylether, anesterization method (Manufacturing Method G) of a (meth)acrylic acidalkaline (earth) metal salt and a halogen-containing vinylether, avinylexchanging method (Manufacturing Method H) of a hydroxylradical-containing (meth)acrylic acid ester and a carboxylic acid vinyl,and an ether exchanging method (Manufacturing Method I) of a hydroxylradical-containing (meth)acrylic acid ester and an alkyl vinylether.

Among them, in order to further obtain a desired effect of theembodiment, the Manufacturing Method E is preferred.

Polymerizable Compounds Other than Monomer A

In addition, besides the aforementioned monomer A, various types ofmonofunctional, bifunctional, trifunctional, or higher multifunctionalmonomers and oligomers in the related art may be used (hereinafter,referred to as “other polymerizable compounds”). The monomer mayinclude, for example, a (meth)acryl acid, unsaturated carboxylic acidssuch itaconic acid, crotonic acid, isocrotonic acid, and maleic acid orsalts thereof, esters, urethanes, amides and anhydrides thereof,acrylonitril, styrene, various types of unsaturated polyesters,unsaturated polyethers, unsaturated polyamides, and unsaturatedurethanes. In addition, the oligomer may include, for example, anoligomer made from the aforementioned monomer such as a straight-chainacryl oligomer, an epoxy (meth)acrylate, an oxetane (meth)acrylate, analiphatic urethane (meth)acrylate, an aromatic urethane (meth)acrylate,an polyester (meth)acrylate.

In addition, as another monofunctional monomer or multifunctionalmonomer, an N-vinylcompound may be contained. The N-vinylcompound mayinclude N-vinylformamide, N-vinylcarbazole, N-vinylacetamide,N-vinylpyrrolidone, N-vinylcaprolactam, acryloyl morpholine, derivativesthereof, and the like.

Among other polymerizable compounds, an ester of a (meth)acryl acid,this is, a (meth)acrylate is preferred.

Among the (meth)acrylates described above, the monofunctional(meth)acrylate may include, for example, isoamyl (meth)acrylate, stearyl(meth)acrylate, lauryl (meth)acrylate, octyl (meth)acrylate, decyl(meth)acrylate, isomiristyl (meth)acrylate, isostearyl (meth)acrylate,2-ethyl hexyl diglycol (meth)acrylate, 2-hydroxybutyl (meth)acrylate,butoxy ethyl (meth)acrylate, ethoxydiethylene glycol (meth)acrylate,methoxydiethylene glycol (meth)acrylate, methoxy polyethylene glycol(meth)acrylate, methoxypropylene glycol (meth)acrylate, phenoxyethyl(meth)acrylate, tetrahydrofurfuryl (meth)acrylate, isobornyl(meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl(meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate,lactone-modified flexible (meth)acrylate, t-butyl cyclohexyl(meth)acrylate, dicyclopentanyl (meth)acrylate, and dicyclopentenyloxyethyl (meth)acrylate. Among the materials, in order to secure goodcompatibility with the additive agents, phenoxyethyl (meth)acrylate ispreferred.

Among the (meth)acrylates described above, the bifunctional(meth)acrylate may include, for example, triethylene glycoldi(meth)acrylate, tetraethylene glycol di(meth)acrylate, polyethyleneglycol di(meth)acrylate, dipropylene glycol di(meth)acrylate,tripropylene glycol di(meth)acrylate, polypropylene glycoldi(meth)acrylate, 1,4-butane diol di(meth)acrylate, 1,6-hexane dioldi(meth)acrylate, 1,9-nonane diol di(meth)acrylate, neopentyl glycoldi(meth)acrylate, diemethylol tricyclodecane di(meth)acrylate, EO(ethylene oxide) additive di(meth)acrylate of bisphenol A, PO (propyleneoxide) additive di(meth)acrylate of bisphenol A, hydroxy pivalic acidneopentyl glycol di(meth)acrylate, and polytetramethylene glycoldi(meth)acrylate. Among the materials, in order to obtain a robustcoated film and to secure low viscosity, dipropylene glycoldi(meth)acrylate is preferred.

Among the (meth)acrylates described above, the multifunctional(meth)acrylate such as trifunctional or higher (meth)acrylate mayinclude, for example, trimethylol propane tri (meth)acrylate, EOmodified trimethylol propane tri (meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritolhexa (meth)acrylate, ditrimethylol propane tetra(meth)acrylate, glycerylpropoxy tri (meth)acrylate, caprolactone modified trimethylol propanetri (meth)acrylate, pentaerythritol ethoxy tetra(meth)acrylate, andcaprolactam modified dipentaerythritol hexa (meth)acrylate. Among thematerials, in order to obtain a robust coated film and to secure goodcurability, trimethylol propane tri (meth)acrylate is preferred.

In addition, among the materials, other polymerizable compoundspreferably contain a monofunctional (meth)acrylate. In this case, theviscosity of the ink composition becomes low, the solubility to additiveagents other than the photopolymerization initiator becomes excellent,and it is possible to obtain ejection stability during the ink jetrecording period. In addition, in order to improve robustness, heatresistance, and chemical resistance of the coated film, a combination ofthe monofunctional (meth)acrylate and the bifunctional (meth)acrylate ismore preferred.

In addition, it is preferable that the monofunctional (meth)acrylatehave one or more types of skeletons selected from a group consisting ofan aromatic ring skeleton, a saturated alicyclic skeleton, and aunsaturated alicyclic skeleton. By allowing the aforementioned otherpolymerizable compound to be the monofunctional (meth)acrylate having askeleton, the viscosity of the ink composition may be lowered.

The monofunctional (meth)acrylate having an aromatic ring skeleton mayinclude, for example, phenoxyethyl (meth)acrylate and2-hydroxy-3-phenoxypropyl (meth)acrylate. In addition, themonofunctional (meth)acrylate having a saturated alicyclic skeleton mayinclude, for example, isobornyl (meth)acrylate, t-butyl cyclohexyl(meth)acrylate and dicyclopentanyl (meth)acrylate. In addition, themonofunctional (meth)acrylate having a unsaturated alicyclic skeletonmay include, for example, dicyclopentenyl oxyethyl (meth)acrylate.

Among the materials, in order to reduce the viscosity and a bad oder, atleast one of phenoxyethyl (meth)acrylate and isobornyl (meth)acrylate ispreferred, and the phenoxyethyl (meth)acrylate is more preferred.

In the case where the ink composition according to the embodimentcontains a polymerizable compound besides the monomer A, the containedamount of the polymerizable compound preferably in a range of equal toor more than 10 wt % with respect to the total amount of the inkcomposition (100 wt %), more preferably in a range of equal to or morethan 20 wt %. In addition, the contained amount is preferably in a rangeof equal to or less than 55 wt %, more preferably in a range of equal toor less than 45 wt %, furthermore preferably in a range of equal to orless than 40 wt %. In addition, particularly, in the case where thephenoxyethyl (meth)acrylate is contained as the polymerizable compound,the contained amount is preferably in a range of equal to or more than10 wt % with respect to the total amount of the ink composition (100 wt%), more preferably in a range of equal to or more than 20 wt %. Inaddition, the contained amount is preferably in a range of equal to orless than 50 wt %, more preferably in a range of equal to or less than40 wt %. As the contained amount of the phenoxyethyl (meth)acrylate isincreased, the solubility of the additive agent becomes excellent, andthe robustness, heat resistance, and chemical resistance of the coatedfilm become excellent. In addition, as the contained amount ofphenoxyethyl (meth)acrylate is decreased, other constituents in the inkcomposition may be allowed to be increased.

With respect to the aforementioned polymerizable compound, one speciesmay be individually used, or two or more species may be simultaneouslyused.

Photopolymerization Initiator

The photopolymerization initiator contained in the ink compositionaccording to the embodiment is used to perform printing by curing theink existing on the surface of the recording medium by thephotopolymerization through illumination of the ultraviolet rays. Byusing the ultraviolet rays (UV) among radioactive rays, it is possibleto obtain excellent stability and to suppress the cost of the lightsource lamp.

Acylphosphine Oxide

The photopolymerization initiator according to the embodiment containsan acylphosphine oxide. Therefore, the curability of the ink becomesexcellent, and the degree of initial coloration of the cured filmbecomes low.

The acylphosphine oxide is not particularly limited, but it may include,for example, 2,4,6-trimethyl benzoyl diphenyl phosphine oxide,2,4,6-triethyl benzoyl diphenyl phosphine oxide, 2,4,6-tri phenylbenzoyl diphenyl phosphine oxide, bis(2,4,6-trimethyl benzoyl)phenylphosphine oxide, and bis-(2,6-dimethoxybenzoyl)-2,4,4-trimethyl pentylphosphine oxide.

A commercialized product of the acylphosphine oxide-basedphotopolymerization initiator may include, for example, DAROCUR TPO(2,4,6-trimethyl benzoyl-diphenyl-phosphine oxide), IRGACURE 819(bis(2,4,6-trimethyl benzoyl)phenyl phosphine oxide), and CGI 403(bis(2,6-dimethoxybenzoyl)-2,4,4-trimethyl pentyl phosphine oxide).

In addition, the aforementioned acylphosphine oxide includes a monoacylphosphine oxide. Therefore, the light curing is performed in thestate where the photopolymerization initiator is sufficiently dissolved,and the curability of the ink becomes excellent.

The mono acylphosphine oxide is not particularly limited, but it mayinclude, for example, 2,4,6-trimethyl benzoyl diphenyl phosphine oxide,2,4,6-triethyl benzoyl diphenyl phosphine oxide, and 2,4,6-tri phenylbenzoyl diphenyl phosphine oxide. Among the materials, the2,4,6-trimethyl benzoyl-diphenyl-phosphine oxide is preferred.

A commercialized product of the mono acylphosphine oxide-basedphotopolymerization initiator may include, for example, DAROCUR TPO(2,4,6-trimethyl benzoyl-diphenyl-phosphine oxide).

With respect to the photopolymerization initiator according to theembodiment, in order to secure excellent solubility to the polymerizablecompound and excellent internal curability of the coated film and toreduce the degree of initial coloration, the mono acylphosphine oxide ora mixture of the mono acylphosphine oxide and the bisacylphosphine oxideis preferred.

In addition, the aforementioned bisacylphosphine oxide is notparticularly limited, but it may include, for example,bis(2,4,6-trimethyl benzoyl)phenyl phosphine oxide andbis-(2,6-dimethoxybenzoyl)-2,4,4-trimethyl pentyl phosphine oxide. Amongthe materials, the bis(2,4,6-trimethyl benzoyl)phenyl phosphine oxide ispreferred.

The contained amount of the acylphosphine oxide is in a range of 7 to 12wt % with respect to the total amount of the ink composition (100 wt %),preferably in a range of 9 to 12 wt %, more preferably in a range of 10to 11 wt %. If the contained amount is within this range, the curabilityof the ink becomes excellent, and the degree of initial coloration ofthe cured film becomes low.

In addition, the contained amount of the mono acylphosphine oxide ispreferably in a range of equal to or more than 10 wt % with respect tothe total amount (100 wt %) of the acylphosphine oxide, more preferablyin a range of equal to or more than 50 wt %. If the contained amount iswithin this range, the curability of the ink becomes excellent, and thedegree of initial coloration of the cured film becomes low.

In addition, the ink composition according to the embodiment may furthercontain other photopolymerization initiators besides the acylphosphineoxide. As other photopolymerization initiators, for example, an alkylphenone-based photopolymerization initiator, a titanocene-based alkylphenone-based photopolymerization initiator, an oxime ester-basedphotopolymerization initiator, an oxyphenyl acetic acid ester-basedphotopolymerization initiator, and the like are considered.

Polymerization Accelerator

The ink composition according to the embodiment may further contain apolymerization accelerator. The polymerization accelerator is notparticularly limited, but it may include, for example, thioxanthonecompounds such as thioxanthone, 2-methyl thioxanthone, 2,4-diethylthioxanthone, 2-isopropyl thioxanthone, 2-chloro thioxanthone, and2,4-diethyl thioxanthone and amine compounds such as triethanol amine,methyl diethanol amine, triisopropanol amine, 4,4′-dimethyl aminobenzophenone, 4,4′-diethyl amino benzophenone, 2-dimethyl amino benzoicacid ethyl, 4-dimethyl amino benzoic acid ethyl, 4-dimethyl aminobenzoic acid isoamyl, 4-dimethyl amino benzoic acid (n-butoxy) ethyl,4-dimethyl amino benzoic acid 2-ethyl hexyl, and triphenyl amine.

Among the materials, in order to secure a low degree of initialcoloration of the cured film, the thioxanthone compound is preferred.Among the thioxanthone compounds, in order to secure excellentsensitization effect to the acylphosphine oxide, and excellentsolubility to the polymerizable compound, and excellent stability, the2,4-diethyl thioxanthone is preferred.

A commercialized product of the thioxanthone compound may include, forexample, KAYACURE DETX-S (2,4-diethyl thioxanthone) (trade name ofproduct manufactured by NIPPON KAYAKU CO. LTD.), ITX (manufactured byBASF), and Quantacure CTX (manufactured by, ACETO CHEMICAL).

The contained amount of the thioxanthone compound is preferably in arange of 0.5 to 5 wt % with respect to the total amount of the inkcomposition (100 wt %), more preferably in a range of 0.5 to 4 wt %,furthermore preferably in a range of 0.5 to 2 wt %. If the containedamount is within this range, the curability of the ink becomesexcellent, the degree of initial coloration of the cured film becomeslow, and the color stability becomes excellent.

Coloring Material

The ink composition according to the embodiment may further contain acoloring material. With respect to the coloring material, at least oneof a pigment and a dye may be used.

Pigment

In the embodiment, a pigment may be used as the coloring material, sothat it is possible to improve the light resistance of the inkcomposition. With respect to the pigment, both of an inorganic pigmentand an organic pigment may be used.

As the inorganic pigment, carbon black (C. I. Pigment Black 7) such as afurnace black, a lamp black, an acetylene black, and a channel black,iron oxide, and titanium oxide may be used.

The organic pigment may include azo pigments such as insoluble azopigments, condensed azo pigments, azoreki, chelate azo pigments,polycyclic pigments such as phthalocyanine pigments, perylene andperinone pigments, anthraquinone pigments, quinacridone pigments,dioxane pigments, thioindigo pigments, isoindolinone pigments, andquinophthalone pigments, dye chelates (for example, basic dye typechelates, acidic dye type chelates, or the like), stained lakes (basicdye type lakes, acidic dye type lakes), nitro pigments, nitrosopigments, aniline blacks, and daylight fluorescent pigments.

More specifically, the carbon black used as the black ink may includeNo. 2300, No. 900, MCF88, No. 33, No. 40, No. 45, No. 52, MA7, MA8,MA100, No. 2200B, and the like (trade names of products manufactured byMITSUBISHI CHEMICAL CORPORATION), Raven 5750, Raven 5250, Raven 5000,Raven 3500, Raven 1255, Raven 700, and the like (trade names of productsmanufactured by CARBON COLUMBIA), Regal 400R, Regal 330R, Regal 660R,Mogul L, Monarch 700, Monarch 800, Monarch 880, Monarch 900, Monarch1000, Monarch 1100, Monarch 1300, Monarch 1400, and the like (tradenames of products manufactured by CABOT JAPAN K.K.), and Color BlackFW1, Color Black FW2, Color Black FW2V, Color Black FW18, Color BlackFW200, Color Black S150, Color Black S160, Color Black S170, Printex 35,Printex U, Printex V, Printex 140U, Special Black 6, Special Black 5,Special Black 4A, Special Black 4, and the like (trade names of productsmanufactured by DEGUSSA).

The pigment used as the white ink may include C. I. Pigment White 6, 18,21.

The pigment used as the yellow ink may include C. I. Pigment Yellow 1,2, 3, 4, 5, 6, 7, 10, 11, 12, 13, 14, 16, 17, 24, 34, 35, 37, 53, 55,65, 73, 74, 75, 81, 83, 93, 94, 95, 97, 98, 99, 108, 109, 110, 113, 114,117, 120, 124, 128, 129, 133, 138, 139, 147, 151, 153, 154, 167, 172,180.

The pigment used as the magenta ink may include C. I. Pigment Red 1, 2,3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 17, 18, 19, 21, 22, 23, 30,31, 32, 37, 38, 40, 41, 42, 48 (Ca), 48 (Mn), 57 (Ca), 57:1, 88, 112,114, 122, 123, 144, 146, 149, 150, 166, 168, 170, 171, 175, 176, 177,178, 179, 184, 185, 187, 202, 209, 219, 224, 245, or C. I. PigmentViolet 19, 23, 32, 33, 36, 38, 43, 50.

The pigment used as the cyan ink may include C. I. Pigment Blue 1, 2, 3,15, 15:1, 15:2, 15:3, 15:34, 15:4, 16, 18, 22, 25, 60, 65, 66, or C. I.Vat Blue 4, 60.

In addition, the pigment excluding the magenta, cyan and yellow pigmentsmay include, for example, C. I. Pigment Green 7, 10, C. I. Pigment Brown3, 5, 25, 26, or C. I. Pigment Orange 1, 2, 5, 7, 13, 14, 15, 16, 24,34, 36, 38, 40, 43, 63.

With respect to the pigment, one species may be individually used, ortwo or more species may be simultaneously used.

In the case where the aforementioned pigment is used, the averageparticle diameter is preferably equal to or less than 2 μm, morepreferably in a range of 30 to 300 nm. If the average particle diameteris within the aforementioned range, reliability such as ejectionstability or dispersion stability of the ink composition may become moreexcellent, and an image having an excellent quality of image may beformed. Herein, in the specification, the average particle diameter ismeasured by a dynamic light scattering method.

Dye

In the embodiment, a dye may be used as the coloring material. The dyeis not particularly limited, and an acidic dye, a direct dye, a reactivedye, and a basic dye may be used. The dye may include, for example, C.I. Acid Yellow 17, 23, 42, 44, 79, 142, C. I. Acid Red 52, 80, 82, 249,254, 289, C. I. Acid Blue 9, 45, 249, C. I. Acid Black 1, 2, 24, 94, C.I. Food Black 1, 2, C. I. Direct Yellow 1, 12, 24, 33, 50, 55, 58, 86,132, 142, 144, 173, C. I. Direct Red 1, 4, 9, 80, 81, 225, 227, C. I.Direct Blue 1, 2, 15, 71, 86, 87, 98, 165, 199, 202, C. I. Direct Black19, 38, 51, 71, 154, 168, 171, 195, C. I. Reactive Red 14, 32, 55, 79,249, and C. I. Reactive Black 3, 4, 35.

With respect to the dye, one species may be individually used, or two ormore species may be simultaneously used.

In order to secure good chromogenic property and to suppress thedeterioration of the curing of the coated film due to the lightabsorption of the coloring material itself, the contained amount of thecoloring material is preferably in a range of 1 to 20 wt % with respectto the total amount of the ink composition.

Dispersing Agent

In the case where the ink composition according to the embodimentcontains the pigment, the ink composition may further contain adispersing agent in order to secure good pigment dispersability. Thedispersing agent is not particularly limited, but it may include, forexample, a dispersing agent such as a macromolecular dispersing agentwhich is well used to manufacture a pigment dispersion liquid. Aspecific example may include one or more species of polyoxy alkylenepolyalkylene polyamine, a vinyl-based polymer and a copolymer, anacryl-based polymer and a copolymer, a polyester, a polyamide, apolyimide, a poly urethane, an amino-based polymer, a silicon-containingpolymer, an sulfur-containing polymer, a fluorine-containing polymer,and an epoxy resin as a main constituent. A commercialized product ofthe macromolecular dispersing agent may include Ajisper series (tradename) manufactured by AJINOMOTO FINE TECHNO CO., INC., Solsperse series(Solsperse 36000 or the like, trade name) available from AVECIA CO.,Disperbyk series (trade name) manufactured by BYK CHEMIE, and Disperonseries (trade name) manufactured by KUSUMOTO CHEMICALS CO.

Leveling Agent

The ink composition according to the embodiment may further contain aleveling agent (surfactant) in order to secure good wettability withrespect a printing base material. The leveling agent is not particularlylimited, but for example, as a silicon-based surfactant, polyestermodified silicon or polyether modified silicon may be used. It isparticularly preferable that polyether modified polydimethyl siloxane orpolyester modified polydimethyl siloxane are used. A specific examplemay include BYK-347, BYK-348, BYK-UV3500, 3510, 3530, 3570 (trade nameof product manufactured by BYK JAPAN K.K.).

Polymerization Inhibitor

The ink composition according to the embodiment may further contain apolymerization inhibitor in order to secure good preservation stabilityof the ink composition. The polymerization inhibitor is not particularlylimited, but for example, IRGASTAB UV10 and UV22 (trade names ofproducts manufactured by BASF), hydroquinone monomethyl ether (MEHQ,trade names of products manufactured by KANTO CHEMICAL CO., INC.) may beused.

Other Additive Agents

The ink composition according to the embodiment may contain otheradditive agents (constituents) besides the aforementioned additiveagents. These constituents are not particularly limited, but mayinclude, for example, a penetration enhancer, a wetting agent(humectant), and other additive agents which are well known in therelated art. Other additive agents listed above may include, forexample, a fixer, a fungicide, an antiseptic agent, an antioxidant, anultraviolet ray absorber, a chelate agent, a pH adjuster, and aviscosity improver which are well known in the related art.

In addition, as described later, the ink composition according to theembodiment may be cured through illumination of ultraviolet rays ofwhich the light emitting peak wavelength is in a range of 350 to 400 nmwith an illumination energy of less than 300 mJ/cm².

Recording Medium

A recording material may be obtained by ejecting the UV curable type inkcomposition according to the embodiment on the recording medium by arecording method described later. The recording medium may include, forexample, an absorptive recording medium or a non-absorptive recordingmedium. The recording method according to an embodiment described belowmay be applied to a variety of the recording media having variousabsorption performances ranging from a non-absorptive recording mediumwhich may be easily penetrated by penetrate an aqueous ink compositionthereto to an absorptive recording medium which may not be easilypenetrated by an aqueous ink composition hereinto. However, in the casewhere the ink composition is applied to the non-absorptive recordingmedium, a drying process may be necessarily provided after the curingthrough the illumination of the ultraviolet rays.

The absorptive recording medium is not particularly limited, but it mayinclude, for example, a plain paper such an electro-photographic paperhaving a high permeability of aqueous ink, ink jet paper (ink jetdedicated paper having an ink absorption layer made from silicaparticles or alumina particles or an ink absorption layer made from ahydrophilic polymer such as polyvinylalcohol (PVA) orpolyvinylpyrrolidone (PVP)), art paper used for general offset printinghaving a relatively low permeability of aqueous ink, coat paper, castpaper, and the like.

The non-absorptive recording medium is not particularly limited, but itmay include, for example, a plastic film or plate such as polyvinylchloride (PVC), polyethylene, polypropylene, and polyethyleneterephthalate (PET), a metal plate such as iron, silver, copper, andaluminum, a metal plate or a plastic film produced by depositing variousmetals, an alloy plate such as stainless steel or brass, or the like.

Recording Method

An embodiment of the invention relates to a recording method. The UVcurable type ink composition according to the embodiment may be used forthe recording method according to the embodiment. An ink jet type may beapplied to the recording method. The recording method includes anejection process for ejecting an ink composition on a recording mediumand a curing process for curing the ink composition by illuminating theink composition ejected by the ejection process with an ultravioletrays. In this manner, a coated film (cured film) is formed with the inkcomposition cured on the recording medium.

Ejection Process

In the ejection process, the ink composition is ejected on the recordingmedium, and the ink composition is attached to the recording medium. Atthe time of ejecting the ink composition, the viscosity of the inkcomposition is preferably in a range of equal to or less than 15 mPa·s,more preferably in a range of 3 to 10 mPa·s. If the viscosity of an inkcomposition is within the aforementioned range in the state thetemperature of the ink composition is set to the room temperature or theink composition is not heated, the ink composition may be ejected in thestate where the temperature of the ink composition is set to the roomtemperature or the ink composition is not heated. On the other hand, theviscosity of the to-be-ejected ink composition may be allowed to have apreferable viscosity by heating the ink composition at a predeterminedtemperature. In this manner, good ejection stability may be obtained.

Since the viscosity of radioactive ray curable type ink compositionaccording to the embodiment is higher than that of an aqueous inkcomposition which is used as a general ink-jet ink, the viscosity isgreatly changed according to a change in temperature at the time ofejection. The change in viscosity of the ink has much influence on achange in size of liquid droplets and a change in ejection rate ofliquid droplets, and furthermore, it may lead to deterioration inquality of image. Therefore, it is preferable that the temperature ofthe ink at the time of ejection is maintained to be as constant aspossible.

Curing Process

Next, in the curing process, the ink composition ejected and attached onthe recording medium is cured through illumination of the ultravioletrays (light). This is because the photopolymerization initiatorcontained in the ink composition is dissolved through illumination ofthe ultraviolet rays to generate initiating species such as radicals,acids, and bases and the polymerization reaction of thephotopolymerizable compound is prompted by the function of theinitiating species. Otherwise, this is because the polymerizationreaction of the photopolymerizable compound is initiated through theillumination of the ultraviolet rays (light). At this time, if asensitizing dye together with the photopolymerization initiator exist inthe ink composition, the sensitizing dye in the system absorbs activeradioactive rays to be in the excited state, and the dissolution of thephotopolymerization initiator is precipitated by allowing thesensitizing dye to be in contact with the photopolymerization initiator,so that it is possible to achieve the more sensitive curing reaction.

As an ultraviolet ray source, a mercury lamp, a gas-solid laser, and thelike are mainly used. As a light source used for the curing of the UVcurable type ink-jet ink composition, a mercury lamp and an a metalhalide lamp are widely known. On the other hand, currently, mercury-freesources are greatly preferred in terms of environmental protection, andreplacement with a GaN-based semiconductor ultra violet light emittingdevice is very useful from industrial and environmental points of view.In addition, the ultraviolet ray light emitting diode (UV-LED) and theultraviolet ray laser diode (UV-LD) has a small size, a long lifetime,and a high efficiency and is inexpensive, and thus, these sources areexpected to be used as a UV curable type ink jet light source. Among thesources, the UV-LED is preferred.

Herein, it is preferable that a UV curable type ink composition whichmay be cured by using a UV-LED of which the light emitting peakwavelength is preferably in a range of 350 to 400 nm, more preferably ina range of 370 to 400 nm with an illumination energy which is preferablyin a range of less than 300 mJ/cm², more preferably in a range of lessthan 200 mJ/cm² be used. In this case, it is possible to lower the costand to obtain high printing speed. Such an ink composition may beobtained by containing at least one of a photopolymerization initiatorwhich is dissolved through the ultraviolet ray illumination in thewavelength range and a polymerizable compound of which thepolymerization is initiated through the ultraviolet ray illumination inthe wavelength range.

In this manner, according to the two embodiment described above, it ispossible to provide a UV curable type ink composition which has a lowdegree of initial coloration, excellent curability (curing rate) of theink, excellent abrasion resistance of the cured film, and excellentcolor stability, and a recording method using the UV curable type inkcomposition. In addition, with respect to the UV curable type inkcomposition according to the embodiment, it is possible to obtainparticularly desired effect in the light curing through illumination ofthe ultraviolet rays of which the light emitting peak is in a range of350 to 400 nm.

Examples

Hereinafter, although the embodiments of the first invention aredescribed more in detail by using examples and comparative examples, theembodiments are not limited to these examples.

Constituents Used

The constituents used in the following examples and comparative examplesare as follows.

Monomer A

acryl acid 2-(2-vinyloxyethoxy) ethyl (VEEA[trade name], manufactured byNIPPON SHOKUBAI CO., LTD., abbreviated to VEEA in Tables 1 and 2)

Compound B

dipentaerythritol hexa acrylate (A-DPH [trade name], manufactured bySHIN-NAKAMURA CHEMICAL CO., abbreviated to DPHA in Tables 1 and 2)

dipentaerythritol pentaacrylate (SR399 [trade name], manufactured bySARTOMER, abbreviated to DPPA in Tables 1 and 2)

Monofunctional (Meth)Acrylate C

phenoxyethyl acrylate (Biscoat #192 [trade name], manufactured by OSAKAORGANIC CHEMICAL INDUSTRY LTD., abbreviated to PEA in Tables 1 and 2)

benzyl acrylate (FA-BZA [trade name], manufactured by HITACHI CHEMICALCO., abbreviated to BA in Tables 1 and 2)

isobornyl acrylate (IBXA [trade name], manufactured by OSAKA ORGANICCHEMICAL INDUSTRY LTD., abbreviated to IBXA in Table 1)

Other Polymerizable Compounds

ditrimethylol propane tetraacrylate (SR355 [trade name], manufactured bySARTOMER, abbreviated to DTMPTA in Tables 1 and 2)

trimethylol propane triacrylate (SR351S [trade name], manufactured bySARTOMER, abbreviated to TMPTA in Tables 1 and 2)

Photopolymerization Initiator

IRGACURE 819 (trade names of products manufactured by BASF, solidcontent 100%, abbreviated to 819 in Tables 1 and 2)

DAROCURE TPO (trade names of products manufactured by BASF, solidcontent 100%, abbreviated to TPO in Tables 1 and 2)

KAYACURE DETX-S (trade names of products manufactured by NIPPON KAYAKUCO., LTD., solid content 100%, abbreviated to DETX-S in Tables 1 and 2)

Slip Agent

silicon-based surface conditioner BYK-UV3500 (trade names of productsmanufactured by BYK, abbreviated to UV3500 in Tables 1 and 2)

Polymerization Inhibitor

p-methoxyphenol (MEHQ [trade name], manufactured by KANTO CHEMICAL CO.,INC.)

Pigment

Pigment Blue 15:4 (IRGALITE BLUE GLVO [trade name], manufactured byBASF, abbreviated to blue 15 in Table 1)

Pigment Black 7 (carbon black) (Microlith Black C-K [trade name],manufactured by BASF)

Dispersing Agent

Solsperse 36000 (trade name of product manufactured by LUBRIZOLCORPORATION, abbreviated to Sol36000 in Tables 1 and 2)

Examples 1 to 44

The UV curable type ink-jet ink compositions of cyan (Example 1 to 26,and 44) and black (Examples 27 to 43) are obtained by adding theconstituents listed in the following Tables 1 to 5 so as to have thecomposition (unit: wt %) and stirring the resulting products by ahigh-speed water cooling stirrer.

Evaluation Items

1. Curability of Thin Cured Film

The aforementioned UV curable type ink-jet ink compositions are chargedin nozzle columns by using an ink jet printer PX-G5000 (trade name ofproduct manufactured by SEIKO EPSON CORPORATION). At room temperatureand atmospheric pressure, a thin film-shaped beta pattern image(recording resolution 720×720 dpi) is printed on the PET film (Lumirror125E20 [trade name] manufactured by PANAKKU INC.) by dots of the ink ofwhich the diameter is middle sized so that the thickness of the printedmaterial is in a range of 0.5 to 3 μm, and the beta pattern image iscured through illumination of the ultraviolet rays having anillumination intensity of 60 mW/cm² and a wavelength of 395 nm with theillumination energy of 200 mJ/cm² from the UV-LED in the ultraviolet rayillumination apparatus installed in the side of the carriage.

In this manner, recording materials where the beta pattern image isprinted on the PET film are produced. Herein, the beta pattern imagedenotes an image where dots are recorded with respect to all the pixels,each of which is a minimum recording unit area defined by a recordingresolution.

With respect to the illumination energy [mJ/cm²], the illuminationintensity [mW/cm²] of the illuminated surface which is illuminated withlight from the light source is measured, and the illumination energy iscalculated from a product of the illumination intensity and theillumination continuation time [s]. The illumination intensity ismeasured by using an ultraviolet ray intensity meter UM-10 and alight-receiving unit UM-400 (manufactured by KONICA MINOLTA SENSING,INC.).

The curability of the thin cured film is evaluated by using theillumination energy at the tack-free time as an indicator. Herein, it isdetermined based on the following conditions whether or not tack-freeoccurs. In other words, the occurrence of tack-free is determined basedon whether or not ink is attached to a cotton swab or based on whetheror not a scratch is formed on the ink cured material on the recordingmedium. At this time, the cotton swab used is a Johnson cotton swabmanufactured by JOHNSON & JOHNSON. The scrubbing times is set to 10 asthe reciprocation times, and the scrubbing strength is set to 100 gweight.

The ink coated film (cured film) at the time of evaluation of thecurability is configured as a thin film having a thickness of 0.5 to 3μm. The evaluation results are listed in the following Tables 6 to 10.

AAA: the illumination energy at the tack-free time is equal to or lessthan 100 mJ/cm²

AA: the illumination energy at the tack-free time is more than 100mJ/cm² and equal to or less than 200 mJ/cm²

A: the illumination energy at the tack-free time is more than 200 mJ/cm²and equal to or less than 300 mJ/cm²

B: the illumination energy at the tack-free time is more than 300 mJ/cm²and equal to or less than 400 mJ/cm²

C: the illumination energy at the tack-free time is more than 400 mJ/cm²

2. Curability of Thick Cured Film

The aforementioned UV curable type ink-jet ink compositions are chargedin nozzle columns by using an ink jet printer PX-G5000 (trade name ofproduct manufactured by SEIKO EPSON CORPORATION). At room temperatureand atmospheric pressure, a thick film-shaped beta pattern image(recording resolution 720×720 dpi) is printed on the PET film (Lumirror125E20 [trade name] manufactured by PANAKKU INC.) by dots of the ink ofwhich the diameter is middle sized so that the thickness of the printedmaterial is in a range of 10 to 11 μm, and the beta pattern image iscured through illumination of the ultraviolet rays having anillumination intensity of 60 mW/cm² and a wavelength of 395 nm with theillumination energy of 200 mJ/cm² from the UV-LED in the ultraviolet rayillumination apparatus installed in the side of the carriage. In anexample where the tack-free state is not achieved, the illuminationcontinues to be performed until the tack-free state is achieved.

In this manner, recording materials where the beta pattern image curedup to the tack-free state is printed on the PET film are produced. Inaddition, the tack-free state checking method, the beta pattern image,and the measurement and calculation of the illumination energy and theillumination intensity are the same as those described in the section“Curability of Thin Cured Film”.

The curability of the thick cured film is evaluated by using anindicator indicating what a degree of the wrinkling occurs on the betapattern image (cured film) cured up to the tack-free state. The degreeof occurrence of the wrinkling is observed by visual inspection.

At the time of the curability evaluation, the thickness of the inkcoated film (cured film) is set to be in a range of 10 to 11 μm as athick film. The evaluation results are listed in the following Tables 6to 10.

AAA: No wrinkling occurs.

AA: Wrinkle occurs in an area which is in a range of less than 5% withrespect to the entire cured film.

A: Wrinkle occurs in an area which is in a range of equal to or morethan 5% and equal to or less than 20% with respect to the entire curedfilm.

B: Wrinkle occurs in an area which is in a range of equal to or morethan 20% and equal to or less than 100% with respect to the entire curedfilm.

C: Wrinkle occurs in the entire cured film.

3. Viscosity

The viscosity (mPa·s) of the ink composition is measured at 20° C. byusing a rheometer (MCR-300, trade name of product manufactured byPHYSICA). The evaluation results are listed in the following Tables 6 to10.

AA: equal to or more than 3 mPa·s and equal to or less than 20 mPa·s

A: more than 20 mPa·s and equal to or less than 30 mPa·s

B: more than 30 mPa·s

TABLE 1 Example 1 2 3 4 5 6 7 8 9 10 Monomer A VEEA 5.00 76.81 7.0060.00 60.00 35.00 13.81 73.81 6.00 10.00 Compound B DPHA 35.00 2.0030.00 3.00 32.81 30.00 5.00 DPPA 5.00 42.81 40.00 Other PolymerizableDTMPTA Compound Listed Above TMPTA 8.81 11.81 5.00 PEA BA 35.00 5.0035.00 20.81 18.81 16.00 35.00 5.00 35.00 33.81 IBXA PhotopolymerizationInitiator 819 6.00 6.00 6.00 6.00 6.00 6.00 6.00 6.00 6.00 6.00 TPO 4.804.80 4.80 4.80 4.80 4.80 4.80 4.80 4.80 4.80 DETX-S 2.00 2.00 2.00 2.002.00 2.00 2.00 2.00 2.00 2.00 Slip Agent UV3500 0.13 0.13 0.13 0.13 0.130.13 0.13 0.13 0.13 0.13 Polymerization Inhibitor P-methoxy phenol 0.180.18 0.18 0.18 0.18 0.18 0.18 0.18 0.18 0.18 Pigment Blue 15 2.20 2.202.20 2.20 2.20 2.20 2.20 2.20 2.20 2.20 Carbon black Dispersing AgentSol36000 0.88 0.88 0.88 0.88 0.88 0.88 0.88 0.88 0.88 0.88 Total 100.00100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00

TABLE 2 Example 11 12 13 14 15 16 17 18 19 20 Monomer A VEEA 70.81 48.8135.00 54.48 54.48 80.00 53.81 75.00 49.00 Compound B DPHA 20.00 30.008.81 DPPA 8.00 34.81 Other Polymerizable DTMPTA 12.57 Compound ListedAbove TMPTA 33.81 12.57 PEA 35.00 48.81 16.76 16.76 3.81 BA 5.00 30.00IBXA Photopolymerization Initiator 819 6.00 6.00 6.00 6.00 6.00 6.006.00 6.00 6.00 6.00 TPO 4.80 4.80 4.80 4.80 4.80 4.80 4.80 4.80 4.804.80 DETX-S 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 Slip AgentUV3500 0.13 0.13 0.13 0.13 0.13 0.13 0.13 0.13 0.13 0.13 PolymerizationInhibitor P-methoxy phenol 0.18 0.18 0.18 0.18 0.18 0.18 0.18 0.18 0.180.18 Pigment Blue 15 2.20 2.20 2.20 2.20 2.20 2.20 2.20 2.20 2.20 2.20Carbon black Dispersing Agent Sol36000 0.88 0.88 0.88 0.88 0.88 0.880.88 0.88 0.88 0.88 Total 100.00 100.00 100.00 100.00 100.00 100.00100.00 100.00 100.00 100.00

TABLE 3 Example 21 22 23 24 25 26 27 28 29 30 Monomer A VEEA 75.00 74.0035.00 35.00 10.00 5.00 77.01 7.00 60.00 60.00 Compound B DPHA 5.00 8.0038.81 35.00 1.28 30.00 3.00 DPPA 8.00 8.00 5.00 Other PolymerizableDTMPTA Compound Listed Above TMPTA 8.29 11.29 PEA 3.81 1.81 40.81 40.81BA 35.00 5.00 35.00 20.29 18.29 IBXA 35.00 Photopolymerization Initiator819 6.00 6.00 6.00 6.00 6.00 6.00 6.00 6.00 6.00 6.00 TPO 4.80 4.80 4.804.80 4.80 4.80 4.80 4.80 4.80 4.80 DETX-S 2.00 2.00 2.00 2.00 2.00 3.003.00 3.00 3.00 3.00 Slip Agent UV3500 0.13 0.13 0.13 0.13 0.13 0.13 0.130.13 0.13 0.13 Polymerization Inhibitor P-methoxy phenol 0.18 0.18 0.180.18 0.18 0.18 0.18 0.18 0.18 0.18 Pigment Blue 15 2.20 2.20 2.20 2.202.20 Carbon black 2.00 2.00 2.00 2.00 2.00 Dispersing Agent Sol360000.88 0.88 0.88 0.88 0.88 0.60 0.60 0.60 0.60 0.60 Total 100.00 100.00100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00

TABLE 4 Example 31 32 33 34 35 36 37 38 39 40 Monomer A VEEA 41.00 13.8173.29 5.29 10.00 70.29 48.29 35.00 54.48 Compound B DPHA 33.00 30.005.00 20.00 DPPA 43.00 39.00 8.00 Other Polymerizable DTMPTA 12.57Compound Listed Above TMPTA 4.48 33.29 PEA 35.00 48.29 16.24 BA 9.2935.00 5.00 35.00 34.29 5.00 30.00 IBXA Photopolymerization Initiator 8196.00 6.00 6.00 6.00 6.00 6.00 6.00 6.00 6.00 6.00 TPO 4.80 4.80 4.804.80 4.80 4.80 4.80 4.80 4.80 4.80 DETX-S 3.00 3.00 3.00 3.00 3.00 3.003.00 3.00 3.00 3.00 Slip Agent UV3500 0.13 0.13 0.13 0.13 0.13 0.13 0.130.13 0.13 0.13 Polymerization Inhibitor P-methoxy phenol 0.18 0.18 0.180.18 0.18 0.18 0.18 0.18 0.18 0.18 Pigment Blue 15 Carbon black 2.002.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.20 Dispersing Agent Sol360000.60 0.60 0.60 0.60 0.60 0.60 0.60 0.60 0.60 0.60 Total 100.00 100.00100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00

TABLE 5 Example 41 42 43 44 45 46 47 48 49 Monomer A VEEA 54.48 80.0053.29 75.00 48.88 75.00 74.00 35.00 35.00 Compound B DPHA 30.00 8.295.00 6.00 DPPA 34.41 8.00 8.00 Other Polymerizable DTMPTA CompoundListed Above TMPTA 12.57 PEA 16.24 3.29 3.29 1.29 42.29 40.29 BA IBXAPhotopolymerization Initiator 819 6.00 6.00 6.00 6.00 6.00 6.00 6.006.00 6.00 TPO 4.80 4.80 4.80 4.80 4.80 4.80 4.80 4.80 4.80 DETX-S 3.003.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 Slip Agent UV3500 0.13 0.13 0.130.13 0.13 0.13 0.13 0.13 0.13 Polymerization Inhibitor P-methoxy phenol0.18 0.18 0.18 0.18 0.18 0.18 0.18 0.18 0.18 Pigment Blue 15 Carbonblack 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 Dispersing AgentSol36000 0.60 0.60 0.60 0.60 0.60 0.60 0.60 0.60 0.60 Total 100.00100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00

TABLE 6 Example 1 2 3 4 5 6 7 8 9 10 Evaluation Test Curability (ThinFilm) AA AA AA A A AAA AAA AAA AA AAA Curability (Thick Film) AAA AA AAAA AA AAA AAA AAA AAA AAA Viscosity A AA A AA AA A AA AA A AA

TABLE 7 Example 11 12 13 14 15 16 17 18 19 20 Evaluation Test Curability(Thin Film) AAA C C C C C C C C C Curability (Thick Film) AAA A C C B BC B B B Viscosity AA B AA AA A A AA B AA B

TABLE 8 Example 21 22 23 24 25 26 27 28 29 30 Evaluation Test Curability(Thin Film) B C C C C AA AA AA A A Curability (Thick Film) A B B B B AAAAA AA AA AA Viscosity AA AA AA AA B A AA A AA AA

TABLE 9 Example 31 32 33 34 35 36 37 38 39 40 Evaluation Test Curability(Thin Film) AAA AAA AAA AA AAA AAA C C C C Curability (Thick Film) AAAAAA AAA AAA AAA AAA A C C B Viscosity A AA AA A AA AA B AA AA A

TABLE 10 Example 41 42 43 44 45 46 47 48 49 Evaluation Test Curability(Thin Film) C C C C C B C C C Curability (Thick Film) B C B B B A B B BViscosity A AA B AA B AA AA AA AA

It may be clearly understood from Tables 6 to 10 described above that,the ink compositions (Examples 1 to 11 and 26 to 36) containing at leastone of the VEEA which is one monomer A and the monofunctional(meth)acrylate having an aromatic ring skeleton in which the containedamount is in a range of 5 to 35 wt % in the ink compositions areparticularly excellent in terms of the curability of a thin film incomparison with other ink compositions, and are excellent in terms ofthe curability of a thick film and viscosity.

In addition, it may be understood that the ink compositions containingthe compound B are excellent in terms of, particularly, a thick curedfilm in comparison with the ink compositions containing no compound B.

In addition, it may be clearly understood that, among the inkcompositions which are excellent in terms described above, the inkcompositions where dipentaerythritol hexa acrylate which is in a rangeof 5 to 30 wt % with respect to the total weight of the ink compositionis contained as the compound B are excellent in terms of at least one ofthe curability of a thin cured film and the viscosity in comparison withthe ink compositions where the material outside the above range iscontained.

In addition, it may be clearly understood that, among the inkcompositions which are excellent in terms described above, the inkcompositions where dipentaerythritol pentaacrylate which is in a rangeof 8 to 40 wt % with respect to the total weight of the ink compositionis contained as the compound B are further excellent in terms of both ofthe curability of a thin cured film and the viscosity in comparison withthe ink compositions where the material outside the above range iscontained.

In addition, it may be clearly understood that, among the inkcompositions which are excellent in terms described above, the inkcompositions containing VEEA which is one monomer A which is in a rangeof equal to or less than 75 wt % with respect to the total weight of theink composition are particularly excellent in terms of the curability ofa thin cured film, and the ink compositions containing VEEA which is onemonomer A which is in a range of equal to or more than 10 wt % withrespect to the total weight of the ink composition are particularlyexcellent in terms of the low viscosity.

In addition, with respect to the ink compositions where at least one ofthe phenoxyethyl acrylate and the benzyl acrylate which are themonofunctional (meth)acrylates having an aromatic ring skeleton is notcontained in an amount which is in a range of equal to or more than 5 wt% with respect to the ink composition, the solubility of thephotopolymerization initiator is in poor, and a long time is necessarilytaken to dissolve the photopolymerization initiator. It may beconsidered that the reason why these Examples deteriorate in thecurability of a thin film is that the photopolymerization initiator isnot sufficiently dissolved and the photopolymerization initiator may notsufficiently contribute to the curability. In addition, it is consideredthat, although the ink compositions of these Examples contain thecompound B, the ink compositions of these Examples slightly deterioratein the curability of a thick film in comparison with Examples other thanthe above Examples, and the photopolymerization initiator may notsufficiently contribute to the curability, so that the ink compositionsof these Examples deteriorate in the curability of a thick film.

In addition, the same evaluation as the evaluation of the curabilitywith respect to the aforementioned curability of a thick film isperformed except that the same ink compositions as those of Examples 1and 17 described above and the illumination is performed by using ametal halide lamp instead of the UV-LED. In the case where the same inkcomposition as that of Example 1 is used, the curability of a thick filmis AAA, and in the case where the same ink composition as that ofExample 17 is used, the curability of a thick film is A, but deformationoccurs in the recording medium due to heat released from the metalhalide lamp. It may be understood from these results that, the inkcompositions containing at least one of the VEEA which is one monomer Aand the monofunctional (meth)acrylate having an aromatic ring skeletonin which the contained amount is in a range of 5 to 35 wt % in the inkcompositions and the compound B are good in terms of the curability of athick film even in the case where any type of light source is used incomparison with the ink compositions which do not satisfy all the aboveconditions. Particularly, it may be understood that, even in the casewhere the ink compositions are cured by using UV-LED for which thereleased heat is small, the curability of a thick film become good.

Hereinafter, the embodiment of the second inversion will be specificallydescribed by using Examples and Comparative Examples, but the embodimentis not limited to the Examples.

Constituents Used

The constituents used in Examples and Comparative Examples describedbelow are as follows.

Polymerizable Compound

acryl acid 2-(2-vinyloxyethoxy) ethyl (VEEA, trade name of productmanufactured by NIPPON SHOKUBAI CO. Ltd., abbreviated to VEEA in Tables)

dipropylene glycol diacrylate (APG-100, trade name of productmanufactured by SHIN-NAKAMURA CHEMICAL CO. LTD., abbreviated to DPGDA inTables)

trimethylol propane triacrylate (A-TMPT, trade name of productmanufactured by SHIN-NAKAMURA CHEMICAL CO. LTD., abbreviated to TMPTA inTables)

phenoxyethyl acrylate Biscoat #192 (trade name of product manufacturedby OSAKA ORGANIC CHEMICAL INDUSTRY LTD., abbreviated to PEA in Tables)

Photopolymerization Initiator

IRGACURE 819 (trade name of product manufactured by BASF, abbreviated to819 in Tables)

DAROCUR TPO (trade name of product manufactured by BASF, abbreviated toTPO in Tables)

IRGACURE 907 (trade name of product manufactured by BASF, abbreviated to907 in Tables)

IRGACURE 369 (trade name of product manufactured by BASF, abbreviated to369 in Tables)

IRGACURE 1870 (trade name of product manufactured by BASF, abbreviatedto 1870 in Tables)

Polymerization Accelerator

KAYACURE DETX-S (trade name of product manufactured by NIPPON KAYAKUCO., LTD., abbreviated to DETX-S in Tables)

Pigment

IRGALITE BLUE GLVO (color index name: pigment blue 15:4, trade name ofproduct manufactured by BASF, abbreviated to cyan in Tables)

CROMOPHTAL PinkPT (SA) GLVO (color index name: C. I. Pigment Red 122,trade name of product manufactured by BASF, abbreviated to magenta inTables)

IRGALITE YELLOW LBG (color index name: C. I. Pigment Yellow 13, tradename of product manufactured by BASF, abbreviated to yellow in Tables)

MICROLITH-WA Black C-WA (color index name: C. I. Pigment Black 7, tradename of product manufactured by BASF, abbreviated to black in Tables)

Dispersing Agent

Solsperse 36000 (trade name of product manufactured by LUBRIZOLCORPORATION, abbreviated to Sol36000 in Tables)

Leveling Agent

silicon-based surface conditioner BYK-UV3500 (trade name of productmanufactured by BYK, abbreviated to UV3500 in Tables)

Polymerization Inhibitor

MEHQ (trade name of product manufactured by KANTO CHEMICAL CO., INC.,abbreviated to MEHQ in Tables)

Examples 1 to 18 and Comparative Examples 1 to 15

The UV curable type ink compositions of colors (cyan, magenta, yellow,and black) are obtained by adding the constituents listed in thefollowing Tables so as to have the composition (unit: wt %) listed inthe Tables and stirring the resulting products by a high-speed watercooling stirrer.

TABLE 11 Example 1 2 3 4 5 6 7 Polymerizable VEEA 40 60 80 90 40 40 40Compound DPGDA 0.5 0.5 — — 0.5 0.5 0.5 TMPTA — — — — — — — PEA 40 20 102.2 40 40 40 Photopolymerization 819 6 6 3 — 6 6 6 Initiator TPO 6 6 4 76 6 6 907 — — — — — — — 369 — — — — — — — 1870 — — — — — — — TotalAmount of Photopolymerization 12 12 7 7 12 12 12 InitiatorPolymerization DETX-S 5 5 0.5 0.5 5 5 5 Accelerator Pigment Cyan 2 2 2 —— — — Magenta — — — — 2 — — Yellow — — — — — 2 — Black — — — — — — 2Dispersing Agent Sol36000 0.2 0.2 0.2 — 0.2 0.2 0.2 Leveling AgentUV3500 0.1 0.1 0.1 0.1 0.1 0.1 0.1 Polymerization Inhibitor MEHQ 0.2 0.20.2 0.2 0.2 0.2 0.2 Total 100 100 100 100 100 100 100

TABLE 12 Example 8 9 10 11 12 13 14 15 16 17 18 Polymerizable VEEA 40 4040 40 40 40 40 40 40 40 40 Compound DPGDA 0.5 0.5 0.5 — — 0.5 — — 0.5 —0.5 TMPTA — — — — — — — — — — — PEA 50 50 50 45.5 45.5 50 50 49.5 45 4539 Photopolymerization 819 — 1 6 6 — — — — — 6 6 Initiator TPO 7 6 1 612 7 7 7 7 6 6 907 — — — — — — — — — — — 369 — — — — — — — — — — — 1870— — — — — — — — — — — Total Amount of Photopolymerization 7 7 7 12 12 77 7 7 12 12 Initiator Polymerization DETX-S — — — — — 0.5 1 5 0.5 6Accelerator Pigment Cyan 2 2 2 2 2 2 2 2 2 2 2 Magenta — — — — — — — — —— — Yellow — — — — — — — — — — — Black — — — — — — — — — — — DispersingAgent Sol36000 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 LevelingAgent UV3500 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 PolymerizationInhibitor MEHQ 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 Total 100 100100 100 100 100 100 100 100 100 100

TABLE 13 Comparative Example 1 2 3 4 5 6 7 Polymerizable VEEA — — — — —36 92 Compound DPGDA 40.5 — 80.5 — 0.5 0.5 — TMPTA — 40.5 — 80.5 — — —PEA 40 40 — — 80 44 Photopolymerization 819 6 6 6 6 6 6 — Initiator TPO6 6 6 6 6 6 5 907 — — — — — — — 369 — — — — — — — 1870 — — — — — — —Total Amount of Photopolymerization 12 12 12 12 12 12 5 InitiatorPolymerization DETX-S 5 5 5 5 5 5 0.5 Accelerator Pigment Cyan 2 2 2 2 22 2 Magenta — — — — — — — Yellow — — — — — — — Black — — — — — — —Dispersing Agent Sol36000 0.2 0.2 0.2 0.2 0.2 0.2 0.2 Leveling AgentUV3500 0.1 0.1 0.1 0.1 0.1 0.1 0.1 Polymerization Inhibitor MEHQ 0.2 0.20.2 0.2 0.2 0.2 0.2 Total 100 100 100 100 100 100 100

TABLE 14 Comparative Example 8 9 10 11 12 13 14 15 Polymerizable VEEA 4040 40 40 40 40 40 40 Compound DPGDA 0.5 0.5 0.5 — 0.5 0.5 0.5 0.5 TMPTA— — — — — — — — PEA 50 51 51 44.5 44 50 50 50 Photopolymerization 819 76 — — 6 — — — Initiator TPO — — 6 13 7 — — — 907 — — — — — 7 — — 369 — —— — — — 7 — 1870 — — — — — — — 7 Total Amount of Photopolymerization 7 66 13 7 7 7 7 Initiator Polymerization DETX-S — — — — — — — — AcceleratorPigment Cyan 2 2 2 2 2 2 2 2 Magenta — — — — — — — — Yellow — — — — — —— — Black — — — — — — — — Dispersing Agent Sol36000 0.2 0.2 0.2 0.2 0.20.2 0.2 0.2 Leveling Agent UV3500 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1Polymerization Inhibitor MEHQ 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 Total 100100 100 100 100 100 100 100Evaluation Items1. Curability of Ink

First, the UV curable type ink compositions obtained in Examples 1 to 18and Comparative Examples 1 to 15 are beta-printed on the PET film(resolution 720 dpi×720 dpi) by using a printer (Product NumberPX-G5000, manufactured by SEIKO EPSON CORPORATION). The beta printing isa printing where ink is attached to all the pixels each of which is theminimum unit of printing defined by a resolution.

Next, an image is formed (a recording material is obtained) byilluminating the PET film after the beta printing with the ultravioletrays (center wavelength 395 nm, 300 mW/cm²) by using the ultraviolet rayillumination apparatus (prototype product of inventor's company) wherean LED is installed.

With respect to the accumulated light amount (illumination energy)[mJ/cm²], the illumination intensity [mW/cm²] of the illuminated surfacewhich is illuminated with light from the light source is measured, andthe accumulated light amount (illumination energy) is calculated from aproduct of the illumination intensity and the illumination continuationtime [s]. The illumination intensity is measured by using an ultravioletray intensity meter UM-10 and a light-receiving unit UM-400 (both aremanufactured by KONICA MINOLTA SENSING, INC.).

In addition, it is determined based on the following conditions whetheror not tack-free occurs. In other words, the occurrence of tack-free isdetermined based on whether or not ink is attached to a cotton swab orbased on whether or not a scratch is formed on the ink cured material onthe recording medium. At this time, the cotton swab used is a Johnsoncotton swab manufactured by JOHNSON & JOHNSON. The scrubbing times isset to 10 as the reciprocation times, and the scrubbing strength is setto 100 g weight. In addition, the ink coated film (cured film) at thetime of evaluation of the curability is configured to have a thicknessof 2 μm.

The evaluation standards are as follows. Among the evaluation standards,the standards AA, A, and B are practically allowable. The evaluationresults are listed in the following tables.

AA: the accumulated light amount at the tack-free time is less than 150mJ/cm².

A: the accumulated light amount at the tack-free time is equal to ormore than 150 mJ/cm² and less than 200 mJ/cm².

B: the accumulated light amount at the tack-free time is equal to ormore than 200 mJ/cm² and less than 300 mJ/cm².

C: the accumulated light amount at the tack-free time is equal to ormore than 300 mJ/cm² and less than 400 mJ/cm².

D: the accumulated light amount at the tack-free time is equal to ormore than 400 mJ/cm².

2. Abrasion Resistance of Cured Film

After the obtained recording materials are maintained at 20° C. for 16hours, under the conditions where the weight is 500 g weight andscrubbing times is 100, a scrubber attached with a white cotton cloth(Canequium 3) for scrubbing and the recording material are scrubbed byusing a JSPS-type friction tester robust tester AB-301 (manufactured byTESTER SANGYO CO.), and the surface state of the image is observed byvisual inspection.

The evaluation standards are as follows. Among the evaluation standards,the standards AA, A, and B are practically allowable. The evaluationresults are listed in the following tables.

AA: No scratch occurs on the surface of the image.

A: Scratch occurs in less than 5 sites on the surface of the image.

B: Scratch occurs in equal to or more than 5 sites and equal to or lessthan 10 sites on the surface of the image.

C: Scratch occurs in half of the surface of the image.

D: Scratch occurs in almost the entire surface of the image.

3. Degree of Initial Coloration of Cured Film

With respect to the color of the obtained recording materials,colorimetry is performed by using the CIE Lab (L*a*b* colorimetricsystem). By using the color of the recording material (image) obtainedfrom the ink composition disclosed in Example 4 as a reference, thecolor differences (ΔE) are obtained from the following equation. Thecolorimetry is performed on the recording materials after one hourelapses from the printing.ΔE=(Δa*^2+Δb*^2+ΔL*^2)^(½)

In addition, in Examples 5, 6, and 7, the color differences ΔE areobtained from the color of the recording materials obtained from the inkcompositions (not indicated as Example) which are produced bysubstituting a magenta pigment, a yellow pigment, and a block pigmentfor the cyan pigment in the ink composition disclosed in Example 4.

The evaluation standards are as follows. Among the evaluation standards,the standards AA, A, and B are practically allowable. The evaluationresults are listed in the following tables.

AA: ΔE is less than 1.0.

A: ΔE is equal to or more than 1.0 and less than 1.5.

B: ΔE is equal to or more than 1.5 and less than 2.0.

C: ΔE is equal to or more than 2.0 and less than 2.5.

D: ΔE is equal to or more than 2.5.

4. Color Stability of Cured Film

With respect to the color of the recording materials obtained above,colorimetry is performed by using the CIE Lab (L*a*b* colorimetricsystem). More specifically, the colorimetry is performed on therecording materials which are left to stand for 24 hours after theprinting, and the differences (ΔE) with respect to the color of therecording material just after the printing (that is, the initialrecording material) are obtained from the following equation.ΔE=(Δa*^2+Δb*^2+ΔL*^2)^(½)

The evaluation standards are as follows. Among the evaluation standards,the standards AA, A, and B are practically allowable. The evaluationresults are listed in the following tables.

AA: ΔE is less than 1.0.

A: ΔE is equal to or more than 1.0 and less than 1.5.

B: ΔE is equal to or more than 1.5 and less than 2.0.

C: ΔE is equal to or more than 2.0 and less than 2.5.

D: ΔE is equal to or more than 2.5.

TABLE 15 Example Evaluation Test 1 2 3 4 5 6 7 Curability AA AA A B A AA Abrasion Resistance B A AA AA B B B Degree of A A A AA A A A InitialColoration Color Stability A A AA AA A A A

TABLE 16 Example Evaluation Test 8 9 10 11 12 13 14 15 16 17 18Curability B B B A A B B B AA AA AA Abrasion Resistance B B B B B B B BB B B Degree of A A A B B A AA AA AA A A Initial Coloration ColorStability AA AA AA AA AA AA AA AA A AA B

TABLE 17 Comparative Example Evaluation Test 1 2 3 4 5 6 7 Curability CC D C C B C Abrasion Resistance B B A A D C A Degree of A A A A A A AInitial Coloration Color Stability A A A A A A AA

TABLE 18 Comparative Example Evaluation Test 8 9 10 11 12 13 14 15Curability C C C A A C D C Abrasion Resistance B B B B B B B B Degree ofA A A C C D D C Initial Coloration Color Stability AA AA AA AA AA C C A

In the above tables, the ink compositions of Comparative Examples 3 and4 are not preferable because the solubility of the photopolymerizationinitiator is poor so that long time is taken to dissolve the inkcompositions.

It may be clearly understood from the above tables that the UV curabletype ink compositions where the polymerizable compound contains apredetermined amount of VEEA, the photopolymerization initiator containsa predetermined amount of acylphosphine oxide, and the acylphosphineoxide contains mono acylphosphine oxide have excellent curability, a lowdegree of initial coloration of the cured film, and excellent abrasionresistance and color stability of the cured film. Among the UV curabletype ink compositions described above, it may be clearly understood byreferring to Examples 13 to 18 that the UV curable type ink compositionswhere the thioxanthone compound which is in a range of 0.5 to 5 wt % iscontained as the polymerization accelerator are very excellent in termsof the curability, the a low degree of initial coloration of the curedfilm, and the color stability.

What is claimed is:
 1. A UV curable type ink-jet ink compositioncontaining a monomer A which is expressed by the following generalformula (I):CH2=CR¹—COOR²—O—CH═CH—R³  (I) (in the formula, R¹ is a hydrogen atom ormethyl radical, R² is a bivalent organic residue radical having a carbonnumber in a range of 2 to 20, and R³ is a hydrogen atom or a univalentorganic residue radical having a carbon number in a range of 1 to 11), acompound B containing five or more (meth) acryloyl radicals permolecule, and a monofunctional (meth)acrylate C having an aromatic ringskeleton, wherein the monofunctional (meth)acrylate C which is in arange of 5 to 35 wt % with respect to the total weight of the inkcomposition is contained, wherein the compound B is in a range of 5 to40 wt % with respect to the total of the ink composition, wherein themonomer A is in a range of 10 to 70% with respect to the total weight ofthe ink composition.
 2. The UV curable type ink-jet ink compositionaccording to claim 1, wherein the monomer A is (meth)acrylic acid2-(vinyloxyethoxy)ethyl.
 3. The UV curable type ink-jet ink compositionaccording to claim 1, wherein the compound B contains at least one of ahexa (meth)acrylate compound having six (meth) acryloyl radicals permolecule and a penta(meth)acrylate compound having five (meth) acryloylradicals per molecule.
 4. The UV curable type ink-jet ink compositionaccording to claim 1, wherein the compound B contain a (meth)acrylatehaving a dipentaerythritol skeleton.
 5. The UV curable type ink-jet inkcomposition according to claim 3, wherein the compound B contains adipentaerythritol hexa (meth)acrylate or a dipentaerythritol penta(meth)acrylate.
 6. The UV curable type ink-jet ink composition accordingto claim 1, wherein the monofunctional (meth)acrylate C having anaromatic ring skeleton is at least one of a benzyl (meth)acrylate and aphenoxyethyl (meth)acrylate.
 7. The UV curable type ink-jet inkcomposition according to claim 1, wherein an acylphosphine oxidecompound is contained as the photopolymerization initiator.
 8. The UVcurable type ink-jet ink composition according to claim 7, wherein anacylphosphine oxide compound which is in a range of 7 to 15 wt % withrespect to the total weight of the ink composition is contained as thephotopolymerization initiator.
 9. The UV curable type ink-jet inkcomposition according to claim 1, wherein the curing is performedthrough illumination of ultraviolet rays of which the light emittingpeak wavelength is in a range of 350 to 420 nm with an illuminationenergy of equal to or less than 300 mJ/cm².
 10. The UV curable typeink-jet ink composition according to claim 1, wherein viscosity at 20°C. is in a range of 3 to 30 mPa·s.
 11. The UV curable type ink-jet inkcomposition according to claim 1, wherein the curing is performed in astate of a thin film having a thickness of 0.5 to 3 μm.
 12. An ink jetrecording method of ejecting the UV curable type ink-jet ink compositionaccording to claim 1 on a recording medium and curing the ejected UVcurable type ink-jet ink composition through illumination using a UV-LEDof which the light emitting peak wavelength is in a range of 350 to 420nm.
 13. An ink jet recording apparatus for ejecting the UV curable typeink-jet ink composition according to claim 1 on a recording medium andcuring the ejected UV curable type ink-jet ink composition throughillumination using a UV-LED of which the light emitting peak wavelengthis in a range of 350 to 420 nm.
 14. The UV curable type ink-jet inkcomposition according to claim 1, wherein the monomer A is present in arange of 10 to 41 wt. % with respect to the total weight of the inkcomposition.
 15. The UV curable type ink-jet ink composition accordingto claim 1, wherein the monomer B is present in a range of 5 to 30 wt. %with respect to the total weight of the ink composition.